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Introduction: Before Phishing Had an Inbox
Long before hackers had malware, phishing kits, stolen passwords, or artificial intelligence, there was another kind of attack surface: human trust.
Sherlock Holmes understood that better than most fictional characters of his era. He watched people closely, studied their habits, gathered information before making a move, disguised himself when necessary, and carefully engineered situations that encouraged others to reveal what they knew. He was not breaking into servers because servers did not exist. He was breaking into something arguably more difficult to defend: human decision-making.
That is why Elizabeth Rasnick, assistant professor at the University of West Florida’s Center for Cybersecurity and Artificial Intelligence, used Holmes as the centerpiece of her DEF CON 34 discussion about social engineering. Her argument is both entertaining and deeply relevant to modern cybersecurity: the technology surrounding social engineering has changed dramatically, but the psychology has barely changed at all.
Today’s attacker might use a convincing phishing email, a fake LinkedIn profile, a fraudulent job offer, a deepfake voice, or an AI-generated message. Holmes used disguises, observation, manipulation, relationships, and carefully constructed stories.
The tools are different.
The playbook is remarkably familiar.
The Human Being Is Still the Attack Surface
Modern cybersecurity often focuses on firewalls, endpoint protection, identity systems, encryption, vulnerability management, and increasingly sophisticated artificial intelligence defenses.
Yet one of the most powerful attack vectors can still be sitting in front of a keyboard.
A person can be convinced to click a link.
A person can be persuaded to reveal a password.
A person can approve a fraudulent authentication request.
A person can transfer money to the wrong account.
A person can trust someone who should never have been trusted.
This is why Rasnick describes trust as the “real attack surface.” The statement cuts directly into one of cybersecurity’s most persistent problems: organizations can secure machines far more easily than they can completely predict human behavior.
Technology can determine whether a connection is suspicious.
It is much harder for technology to determine whether a person has been emotionally manipulated.
Sherlock Holmes and the Art of Deception
Elizabeth Rasnick reportedly appeared at DEF CON dressed as Sherlock Holmes, complete with the recognizable deerstalker cap, shawl, and pipe.
The costume was more than a theatrical joke.
It represented the central idea of her presentation.
Holmes repeatedly relied on observation, disguise, intelligence gathering, psychological manipulation, and carefully planned interactions. His investigations often began by learning everything possible about a person or situation before deciding what to do next.
That approach sounds surprisingly familiar to modern cybersecurity professionals.
An attacker rarely begins with the final phishing message.
The preparation often comes first.
Reconnaissance Comes Before Manipulation
One of the most important lessons from both Holmes and modern attackers is simple: know your target.
Cybercriminals increasingly collect information from publicly available sources.
Social media profiles can reveal where someone works, what position they hold, who their colleagues are, which conferences they attend, what projects they discuss, and even when they are likely to be unavailable.
Company websites can reveal organizational structures.
Job advertisements can reveal technology stacks.
Public documents can expose employee names and responsibilities.
Professional networking platforms can reveal reporting relationships.
Individually, these details may seem harmless.
Together, they can become an attack blueprint.
Holmes would observe the environment before making his move. Modern threat actors do essentially the same thing with digital information.
The Attack Begins Before the Phishing Email
A common mistake in cybersecurity awareness is treating phishing as the beginning of an attack.
Often, it is not.
The phishing message may be the final stage of weeks of preparation.
An attacker might first identify an employee in finance, discover their manager, learn when that manager is traveling, determine which communication platform the company uses, and then construct a believable scenario.
The resulting message might say:
“I’m currently in a meeting and need this payment processed immediately.”
The attacker is not merely sending an email.
They are exploiting a previously researched relationship.
Fear, Curiosity and Opportunity Remain Powerful
Human psychology has not received a security patch.
Fear still works.
Curiosity still works.
Urgency still works.
Greed still works.
Empathy still works.
The desire to help a colleague still works.
These emotional triggers are the foundation of countless social engineering attacks.
A victim might be told that their account is about to be suspended.
Another might receive a message claiming that an executive needs urgent assistance.
Someone searching for employment might receive an attractive job offer.
A researcher might receive a document appearing to contain important information.
The technology delivers the message.
Human emotion does much of the work.
Artificial Intelligence Makes the Old Trick More Dangerous
Artificial intelligence has not invented social engineering.
It has industrialized it.
Historically, attackers had to spend considerable time writing convincing messages and researching individual targets. AI can now help generate highly polished text, imitate communication styles, translate messages, create believable conversations, and produce content at enormous scale.
That changes the economics of deception.
A mediocre scam can become a convincing scam.
A campaign aimed at hundreds of people can become a campaign aimed at thousands.
And a generic phishing message can increasingly become personalized.
The fundamental weakness, however, remains the same.
The attacker wants the victim to make a decision.
Holmes Had a Six-Step Playbook
Rasnick’s comparison becomes especially interesting when Holmes’s investigative methods are translated into modern cybersecurity terminology.
The fictional detective repeatedly followed a recognizable sequence.
1. Know the Target
Holmes observed people, environments, relationships, and circumstances.
Modern attackers conduct reconnaissance through publicly available information and compromised data.
2. Become Believable
Holmes used disguises and carefully constructed identities.
Modern criminals use impersonation, spoofed accounts, cloned websites, synthetic voices, and increasingly convincing digital identities.
3. Create a Reason to Act
A target needs a reason to respond.
Attackers manufacture that reason through urgency, authority, fear, curiosity, financial incentives, or emotional pressure.
4. Exploit Emotion
The attacker wants the victim to react instead of carefully analyzing the situation.
Emotion accelerates decision-making.
5. Observe the Reaction
A successful social engineer watches what the victim does next.
The response provides information that can be used to refine the attack.
6. Adapt
If the first approach fails, attackers change tactics.
The same principle applies to Holmes.
The investigation continues until the strategy produces the desired result.
The Red-Headed League Looks Surprisingly Modern
One of the most fascinating comparisons involves “The Red-Headed League.”
In the story, an apparently legitimate organization attracts a target through an unusual opportunity.
The premise may sound old-fashioned, but the underlying concept is strikingly familiar.
Modern attackers frequently create fake companies, fake recruitment agencies, fake employment opportunities, and fraudulent online services to establish credibility before targeting victims.
Fake job scams are particularly effective because they combine two powerful psychological forces: hope and trust.
A person looking for employment may already be motivated to respond quickly.
The attacker only needs to create enough legitimacy to keep that person engaged.
Fake Job Offers Are the New Red-Headed League
Imagine receiving a message from what appears to be a reputable company.
The salary is attractive.
The position matches your skills.
The recruiter has a convincing profile.
The interview process looks professional.
Eventually, the applicant is asked to download a “company application,” complete an identity verification process, or click a document.
At that point, the recruitment process may become the attack.
The target was not necessarily chosen because of technical knowledge.
They were chosen because they were emotionally receptive to the opportunity.
That is social engineering.
Holmes Was Not Automatically the Good Guy
The comparison becomes even more interesting when Sherlock Holmes is placed beside his fictional nemesis, Professor James Moriarty.
Rasnick used the Holmes-Moriarty relationship to illustrate the uncomfortable overlap between ethical hackers and criminals.
Both sides can use reconnaissance.
Both can investigate systems.
Both can manipulate environments.
Both can search for weaknesses.
Both can exploit human behavior.
The critical distinction is not always the technique.
It is intent, authorization and legitimacy.
The Same Technique Can Have Opposite Consequences
Consider reconnaissance.
A penetration tester might research an
A criminal might perform the same research to identify the easiest path into the organization.
The technique itself does not determine whether the action is ethical.
Authorization does.
This is one of the most important lessons for anyone learning cybersecurity.
A security professional may possess exactly the same technical capabilities as an attacker.
What separates them is the boundary around how those capabilities are used.
Ethical Hacking Requires Permission
Rasnick reportedly summarized the difference between ethical and non-ethical hackers as involving the paperwork surrounding the engagement.
That description is deliberately simple, but it highlights a serious point.
A legitimate penetration test has defined scope.
There is an authorization document.
There are rules of engagement.
There are systems that may be tested.
There are systems that may not be touched.
There are reporting requirements.
There are procedures for handling discovered information.
Without authorization, the same activity can cross from security testing into unlawful intrusion.
The keyboard does not know the difference.
The legal agreement does.
The Holmes Lesson for Security Teams
The most important lesson from the presentation is not that organizations should start dressing like Victorian detectives.
It is that cybersecurity programs need to understand people as part of the security architecture.
Employees are not simply the weakest link.
They are also one of the
A properly trained employee can recognize an unusual request.
A suspicious finance worker can stop a fraudulent payment.
A cautious administrator can refuse an unexpected login request.
A well-trained executive can recognize impersonation.
Human judgment can stop an attack that technology misses.
Deep Analysis: How the Sherlock Holmes Playbook Maps to Cybersecurity
Reconnaissance
From a defensive perspective, organizations should understand what information attackers can discover publicly.
Security teams can begin with legitimate asset inventories and authorized reconnaissance.
Identify the organization's known domains dig example.com
Inspect DNS records
dig example.com ANY
Check the security headers of an authorized web server
curl -I https://example.com
These commands should only be used against systems you own or have explicit permission to assess.
Examine Public Exposure
Security teams can review publicly exposed services and assets using approved scanning infrastructure.
For example:
Scan an authorized host for common TCP services nmap -sV example.com
The purpose is not to attack the target.
The purpose is to understand what an attacker might see.
That distinction is fundamental.
Search for Human Exposure
Organizations should also audit publicly available employee information.
Security teams can ask:
Are employee email addresses publicly listed?
Are internal job titles exposed?
Are organizational relationships easy to map?
Are technology platforms disclosed in job advertisements?
Are executive travel schedules publicly visible?
Are internal documents accidentally indexed?
Are employees revealing too much operational information online?
The objective is defensive exposure management.
Detect Suspicious Authentication
Social engineering frequently ends with an attempt to obtain credentials.
Security teams should monitor unusual authentication patterns.
Example defensive Linux log review grep -Ei "failed|invalid|authentication failure" /var/log/auth.log
Organizations using centralized logging should correlate authentication events with device, location, identity, and behavioral signals.
A single failed login may mean nothing.
A sequence of unusual authentication attempts may reveal something much more important.
Strengthen Email Analysis
Security teams can inspect suspicious messages without interacting with potentially malicious links.
Search an exported mail header for common authentication indicators grep -Ei "Authentication-Results|Received:|Return-Path:|Reply-To:" message.txt
Useful indicators include SPF, DKIM, DMARC, sender domains, reply-to addresses, unusual routing, and mismatched identities.
No single signal should automatically be considered definitive.
Build a Human Firewall
The strongest defense against social engineering combines technology with behavioral controls.
Organizations should implement:
phishing-resistant authentication
multifactor authentication
password managers
email security
DMARC enforcement
security awareness training
financial verification procedures
privileged-access controls
strong help-desk verification
incident reporting channels
executive impersonation protection
continuous identity monitoring
The goal is not to make employees suspicious of everything.
It is to make unusual requests harder to execute.
Remove Dangerous Urgency
One of the simplest defensive measures is also one of the most powerful.
Create policies that eliminate artificial urgency.
For example, financial transfers should require independent verification.
Password resets should use established identity verification procedures.
Executives should not be able to bypass security procedures merely because a request appears urgent.
An attacker wants the victim to think:
I have to do this now.
A good security policy gives the employee permission to say:
I need to verify this first.
That small change can destroy an entire attack chain.
Why AI Changes the Scale
Traditional social engineering depended heavily on human labor.
AI reduces that limitation.
Attackers can generate customized messages faster.
They can translate campaigns into multiple languages.
They can simulate professional writing styles.
They can produce variations for different departments.
They can automate follow-up conversations.
They can analyze responses.
This creates a dangerous feedback loop.
The attacker learns from the victim.
The AI helps produce the next message.
The victim responds again.
The attacker adapts.
The cycle continues.
Deepfakes Raise the Stakes
Voice cloning and synthetic video introduce another layer of deception.
Previously, receiving a voice message from an executive might have carried significant credibility.
That assumption is becoming weaker.
A convincing voice is no longer necessarily proof of identity.
A video call is not necessarily proof either.
Organizations therefore need identity verification procedures that do not depend entirely on appearance or voice.
The question is changing from:
Does this sound like my boss?
to:
“Can I independently verify that this request actually came from my boss?”
Trust Should Become Conditional
Cybersecurity does not require eliminating trust.
It requires making trust conditional.
An employee can trust a colleague while still verifying an unusual financial request.
An administrator can trust an executive while still requiring proper authentication.
A recruiter can trust an applicant while still validating documents.
Trust and verification are not opposites.
In modern cybersecurity, they need to work together.
What Undercode Say:
The Technology Changed, the Psychology Did Not
Sherlock Holmes lived in a world without computers, smartphones, social networks, or cloud infrastructure.
Yet many of his investigative techniques map almost perfectly onto today’s threat landscape.
That is because social engineering is fundamentally psychological.
People Are Predictably Unpredictable
Attackers do not need to predict every human behavior.
They only need to understand common behavioral patterns.
People respond to authority.
People respond to urgency.
People want to help.
People become curious.
People fear losing access.
People want attractive opportunities.
Those predictable reactions create opportunities for manipulation.
OSINT Is the Modern Magnifying Glass
Holmes carried tools for observing his environment.
Today’s attacker can gather information without physically approaching the target.
Public websites, social networks, company documents, professional profiles, and leaked information can collectively provide an enormous amount of intelligence.
The internet has effectively turned reconnaissance into a scalable process.
Personalization Makes Attacks Stronger
A generic phishing email is easy to recognize.
A message mentioning your manager, your current project, your company and a real deadline is much harder to dismiss.
Personalization increases credibility.
AI makes personalization cheaper.
That combination is especially concerning.
Social Engineering Is an Attack Chain
A successful scam rarely consists of one message.
It can involve reconnaissance, identity construction, contact, emotional manipulation, credential theft, persistence, and financial exploitation.
Stopping any one stage can break the chain.
That is why layered defense matters.
Security Awareness Alone Is Not Enough
Telling employees to “be careful” is not a complete security strategy.
Employees need practical mechanisms that support good decisions.
They need simple reporting tools.
They need verification procedures.
They need permission to challenge suspicious requests.
They need systems that limit the damage if they make a mistake.
Security Design Should Assume Mistakes
The strongest organizations do not assume that every employee will make the correct decision every time.
They design systems so that one mistake does not become a catastrophe.
Least privilege is an example.
A compromised account should not automatically provide access to everything.
Segmentation is another.
A successful compromise in one department should not immediately expose the entire organization.
MFA Is Valuable, But Not Magical
Multifactor authentication can significantly reduce the value of stolen passwords.
But attackers increasingly target the authentication process itself.
They may attempt to manipulate users into approving fraudulent requests or interact with victims through fake support scenarios.
That is why phishing-resistant authentication methods are increasingly important.
Identity Is Becoming the Battlefield
The modern enterprise perimeter is increasingly built around identities rather than physical networks.
Employees connect from home.
Applications run in the cloud.
Contractors access systems remotely.
Devices move between networks.
The attacker therefore wants identities.
Social engineering is one of the most effective ways to target them.
Help Desks Are High-Value Targets
Attackers understand that technical support staff can reset passwords and modify account access.
A convincing impersonation attempt against a help desk can therefore become an entry point.
Organizations should establish strong identity verification for sensitive requests.
No employee should be able to bypass those controls simply by sounding convincing.
Executives Are Attractive Targets
Executives have authority.
Authority makes impersonation particularly powerful.
A fraudulent message appearing to come from a CEO or CFO can create pressure that ordinary phishing cannot.
Organizations should therefore treat executive impersonation as a serious threat category.
Finance Departments Need Special Protection
Money creates urgency.
Urgency creates mistakes.
Financial teams should have independent verification procedures for sensitive transactions.
A second communication channel can be enough to stop a sophisticated impersonation attempt.
The important part is that the verification method should not depend on the same potentially compromised communication channel.
Curiosity Is an Attack Vector
Security awareness programs often focus on fear.
But curiosity can be just as dangerous.
Confidential salary report.
New employee bonuses.
Private investigation.
Unreleased product information.
The promise of secret information can be extremely effective.
Opportunity Is Another Attack Vector
Fake jobs, investment opportunities, exclusive invitations, and business partnerships can all become delivery mechanisms.
The victim is not always threatened.
Sometimes the victim is tempted.
That distinction matters.
The Best Scam Does Not Look Like a Scam
The most dangerous social engineering attack may look completely normal.
A routine payment request.
A familiar document.
A meeting invitation.
A password reset.
A recruiter contacting a candidate.
A colleague asking for help.
The attack succeeds when the unusual becomes indistinguishable from the ordinary.
Security Teams Need Behavioral Intelligence
Traditional detection looks for malicious files, suspicious IP addresses, and known attack signatures.
Social engineering can produce none of those initially.
Behavioral analysis can therefore become important.
An unusual login followed by an unusual payment request is more concerning than either event alone.
Context matters.
AI Will Increase the Volume of Deception
AI does not need to invent a revolutionary attack technique.
It only needs to make existing techniques cheaper.
If one attacker previously had the capacity to target 100 people, automation may allow that attacker to target thousands.
Scale changes the threat.
AI Also Gives Defenders New Tools
The same technology can help defenders identify suspicious communications, detect anomalies, analyze large volumes of security data, and prioritize investigations.
The future is therefore unlikely to be simply “AI versus humans.”
It will increasingly be AI-assisted attackers versus AI-assisted defenders, with humans still making critical decisions.
Authorization Is the Ethical Boundary
Holmes and Moriarty may use similar investigative techniques, but their intentions are fundamentally different.
That distinction remains essential in cybersecurity.
A penetration tester has permission.
A criminal does not.
The technical action may look similar.
The context changes everything.
Cybersecurity Education Should Teach Judgment
Students learning ethical hacking should understand not only how attacks work, but when they are permitted to perform them.
Technical ability without ethical boundaries can become dangerous.
The strongest cybersecurity professionals understand both capability and responsibility.
The Human Firewall Can Be Strong
Employees are often described as
That description is incomplete.
A well-trained employee can become the final obstacle between an attacker and a successful compromise.
The objective should therefore not be blaming people.
It should be empowering them.
Verification Beats Suspicion
Security teams should not ask employees to distrust everyone.
They should teach employees to verify unusual requests.
That is a more practical and sustainable security culture.
Trust normally.
Verify unusually.
The Holmes Lesson Is Ultimately About Observation
Holmes succeeded because he noticed details other people ignored.
Cybersecurity teams need the same discipline.
An unexpected domain.
An unusual login.
A strange payment request.
A new device.
A changed communication style.
A sudden demand for secrecy.
Small anomalies can become major indicators.
The Attacker Is Studying You
The uncomfortable reality is that social engineering is a two-sided observation game.
The attacker studies the victim.
The defender must study the attacker.
Understanding what information is publicly exposed, what behaviors are predictable, and which processes can be manipulated is therefore essential.
Security Culture Is Part of Infrastructure
Organizations invest enormous amounts of money into technical infrastructure.
They should treat security culture with similar seriousness.
Policies, training, verification procedures and reporting mechanisms are not administrative decorations.
They are defensive infrastructure.
Social Engineering Will Not Disappear
Phishing existed before modern AI.
Impersonation existed before phishing.
Fraud existed before computers.
As long as humans communicate and trust one another, social engineering will remain possible.
Technology can reduce the risk.
It cannot eliminate the underlying psychology.
Holmes Was Ahead of His Time
The irony is that Sherlock Holmes was never really a hacker.
Yet his methods resemble modern reconnaissance, threat intelligence, social engineering and penetration testing.
His greatest tool was not his disguise.
It was his understanding of people.
That may be the most important cybersecurity lesson of all.
✅ Social Engineering Predates the Internet
The article is correct that social engineering did not begin with the internet. Deception, impersonation, manipulation and confidence schemes existed long before computers, while modern technology has simply provided attackers with faster and broader ways to perform them.
✅ Fear and Curiosity Remain Major Manipulation Techniques
The claim that attackers exploit fear, curiosity, urgency and emotional reactions is consistent with well-established social engineering principles. Modern phishing campaigns frequently rely on these psychological triggers rather than purely technical exploitation.
✅ AI Can Increase the Scale of Social Engineering
AI can help attackers generate convincing content, personalize communications and automate parts of campaigns. However, AI is an accelerator rather than the original source of social engineering.
✅ Authorization Separates Ethical Testing From Criminal Intrusion
The
❌ Holmes Was Not Literally a Penetration Tester
Calling Holmes a “modern-day penetration tester” is an analogy rather than a historical or technical fact. His fictional investigations resemble elements of penetration testing and security research, but he obviously did not operate under modern cybersecurity methodologies, contracts or technical standards.
Prediction
(+1) Social Engineering Will Become More Personalized
As AI becomes better at analyzing publicly available information and generating natural communication, phishing and impersonation attempts are likely to become increasingly customized to individual victims.
(+1) Identity Verification Will Become More Important
Organizations will increasingly rely on phishing-resistant authentication, independent verification procedures and behavioral signals rather than trusting usernames, passwords, voices or familiar-looking messages alone.
(+1) Security Training Will Become More Psychological
Future awareness programs will likely focus less on simply identifying suspicious emails and more on understanding manipulation tactics, emotional triggers, authority pressure and artificial urgency.
(+1) Human Judgment Will Remain Critical
Even as AI improves automated detection, attackers will continue targeting human decision-making. Organizations that combine strong technical controls with a security-aware workforce will have a major defensive advantage.
(-1) Deepfakes Will Make Traditional Trust Signals Less Reliable
A familiar voice, profile picture or video call will increasingly be insufficient as proof of identity. Organizations that continue relying on these signals without independent verification will face greater exposure to sophisticated impersonation attacks.
(-1) AI Will Lower the Barrier for Less-Skilled Attackers
Attackers no longer need exceptional writing skills or extensive manual effort to create convincing campaigns. As AI tools become more capable, the number of people able to conduct sophisticated-looking social engineering operations may increase.
(+1) The Sherlock Holmes Principle Will Outlive the Technology
The tools of deception will continue changing, but the fundamental attack remains remarkably stable: learn about the target, become believable, create a reason to act, trigger emotion, observe the response and adapt.
That is why the most important cybersecurity lesson from Sherlock Holmes may not be about computers at all.
It is about people.
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