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Introduction: When Privacy Cannot Protect Availability
A secure messenger can have strong encryption, strict privacy policies, and carefully designed infrastructure, yet still face one fundamental problem: availability.
Threema, the Swiss privacy-focused messaging platform, recently experienced a series of large-scale Distributed Denial-of-Service (DDoS) attacks that disrupted communications for users in multiple countries. The incident did not indicate a compromise of encrypted messages or user accounts. Instead, attackers targeted the infrastructure responsible for keeping the service reachable.
That distinction matters.
In cybersecurity, confidentiality and integrity often receive most of the attention. People want to know whether their messages were stolen, whether accounts were compromised, or whether encryption was broken. But availability is equally important. A messaging service that cannot be reached when people need it is still suffering a serious security incident.
The Threema disruption also highlights another important reality: modern DDoS attacks are no longer simply floods of traffic coming from a handful of obvious sources. Large attacks can involve constantly changing sources, techniques, and traffic patterns, forcing defenders into a continuous battle of adaptation.
For organizations relying on secure communication, the incident is a reminder that cybersecurity is not only about protecting data. It is also about ensuring that critical services remain accessible when somebody actively tries to take them offline.
Threema: A Privacy-Focused Alternative to Mainstream Messaging
Threema is a Swiss paid messaging platform designed around privacy and secure communications. It occupies a similar category to applications such as Signal and WhatsApp, but its business model and privacy positioning have helped it establish a distinct identity among security-conscious users and organizations.
The company also offers business-oriented services, including Threema Work, allowing organizations to use the platform for professional communication.
This makes availability particularly important.
For an individual user, a temporary messaging outage may be an annoyance. For an organization, however, a communications outage can interfere with employees, customers, incident-response teams, and operational workflows.
The Attacks Began With an Apparent Network Problem
Users began reporting problems with Threema on Tuesday evening.
Initially, the company attributed the disruption to a network issue involving its colocation provider. That explanation changed after further investigation revealed that Threema was dealing with a series of DDoS attacks.
The attacks were not limited to one simple traffic pattern.
According to the
What Makes a DDoS Attack So Difficult to Stop?
A traditional denial-of-service attack can sometimes be mitigated by identifying and blocking the source of malicious traffic.
A distributed denial-of-service attack is fundamentally different.
Instead of relying on one system, attackers can generate traffic from a large collection of systems distributed across networks and geographic locations. This makes the attack resemble legitimate distributed Internet traffic.
The defender therefore faces a difficult question: Which traffic should be blocked without accidentally blocking legitimate users?
That becomes even harder when the attacker changes tactics during the incident.
The Cat-and-Mouse Game Behind Modern DDoS Attacks
Threema described the attacks as an ongoing cat-and-mouse game between attackers and defenders.
When defenders identify one traffic pattern and implement a mitigation strategy, attackers can modify their sources, protocols, packet characteristics, traffic volumes, or attack techniques.
The defense must then adapt again.
This cycle can continue for hours or even longer.
The result is not necessarily a spectacular security breach involving stolen data. Sometimes the objective is much simpler: make the service unreliable enough that users cannot depend on it.
Threema Was Unavailable for Several Hours
The most significant disruption occurred Tuesday evening.
According to Threema, the service was unavailable between approximately 7:30 p.m. and 11:30 p.m. CEST, representing roughly four hours of major service disruption.
The situation did not immediately end after that period.
Users continued reporting intermittent problems on Wednesday morning, even though Threema’s status page indicated that the service had returned to normal operation.
Normal operations were eventually restored at approximately 12:23 p.m. CEST.
The Colocation Provider Was Also Targeted
One of the more interesting aspects of the incident is that the attacks also targeted Threema’s colocation partner, Nine.
That introduces another layer of complexity.
If an attacker targets infrastructure shared by multiple customers, the effects can potentially extend beyond one application. Even when an individual company has strong security controls, problems at an upstream provider can create operational consequences.
This is why modern cybersecurity increasingly focuses on dependency risk.
Your organization may be secure while an infrastructure provider, DNS provider, cloud platform, hosting company, CDN, or network carrier experiences an attack.
Threema Could Not Immediately Determine the Primary Target
Threema also acknowledged that it was not completely clear whether the company itself was the primary target.
The attacks may have been directed at multiple targets.
That uncertainty is significant because attribution during an active DDoS event can be difficult. Seeing malicious traffic arrive at a particular infrastructure endpoint does not necessarily reveal the attacker’s ultimate objective.
The attacker may be targeting the application, the provider, a network segment, another customer, or several organizations simultaneously.
The Status Page Had Problems Too
Ironically,
The company explained that the status page was affected by a technical issue unrelated to the DDoS attack.
Because the page could not initially be updated reliably, Threema temporarily took it offline while the problem was resolved.
This created a particularly frustrating situation for users.
When a major online service stops working, users naturally turn to the company’s status page to determine whether the problem is local or widespread. If that communication channel is unavailable, uncertainty increases quickly.
Communication Became Part of the Incident Response
Threema progressively communicated information about the outage through social media.
Business customers using Threema Work received updates through email, while account managers responded to inquiries from customers seeking additional information.
This was an important operational decision.
During an outage, communication is not merely public relations. It becomes part of the security response.
Users need to know whether they should wait, switch to another communication channel, restart devices, investigate their networks, or simply recognize that the problem exists on the provider’s side.
Threema Work Customers Faced Additional Operational Pressure
Organizations using Threema Work depend on the platform differently from casual users.
For businesses, messaging may be part of daily operations, internal coordination, customer communication, or emergency workflows.
An intermittent outage can therefore have a disproportionate impact.
The lesson is straightforward: critical communication platforms should never be treated as the only available communication path.
Organizations should maintain alternative channels for situations in which their primary messaging platform becomes unavailable.
Threema On-Prem Was Not Affected
One of the most important details in the incident is that organizations using Threema On-Prem were not affected by the service disruption.
The reason is architectural.
Threema On-Prem deployments run on the
This does not mean an on-premises deployment is immune to DDoS attacks. An organization could still be attacked directly. However, the dependency chain is different.
That distinction demonstrates the security advantages and trade-offs of controlling infrastructure yourself.
On-Premises Does Not Automatically Mean More Secure
It would be a mistake to interpret the incident as proof that on-premises infrastructure is always superior.
Running infrastructure independently means an organization takes greater responsibility for network security, redundancy, monitoring, DDoS mitigation, patching, backups, and incident response.
A poorly protected on-premises deployment could be easier to disrupt than a professionally protected hosted service.
The real advantage is control and architectural independence, not automatic immunity.
Threema Added Upstream DDoS Protection
Following the attacks, Threema introduced additional specialized DDoS protection.
The company deployed upstream protection designed to filter malicious traffic before it reached its own infrastructure.
This is an important defensive principle.
The closer malicious traffic can be filtered to its origin or upstream network boundary, the less pressure is placed on application servers and internal infrastructure.
Why Upstream Filtering Matters
Imagine an organization with a network capable of processing 10 Gbps of legitimate traffic.
If attackers send 100 Gbps toward the organization, filtering after the traffic has already saturated the organization’s network connection is too late.
The infrastructure may be technically capable of filtering the traffic, but the connection itself becomes the bottleneck.
Upstream filtering changes the equation.
Malicious traffic can be identified and discarded before it consumes the organization’s available bandwidth and infrastructure resources.
The Status Page Is Getting an Upgrade
Threema also plans to improve its status page.
The updated system is expected to include an incident history and an RSS feed that users and Threema Work administrators can subscribe to.
That is more important than it may initially appear.
A reliable status system provides an independent communication path between a service provider and its users.
If the primary application is unavailable, users should still have a trusted mechanism for determining whether an incident is ongoing.
Why an RSS Feed Is Still Useful in 2026
RSS may seem old-fashioned compared with social media notifications, but it has one major advantage.
It is independent.
Users and administrators can subscribe to an external feed without constantly monitoring social networks.
For organizations, this can also support automated monitoring systems that ingest service-status updates and trigger internal alerts.
The humble RSS feed can therefore become part of an organization’s operational resilience strategy.
Deep Analysis: Understanding the Threema DDoS Incident
DDoS Detection Begins With Traffic Baselines
Security teams cannot effectively identify abnormal traffic without understanding what normal traffic looks like.
A basic Linux monitoring command can help administrators observe network interfaces:
ip -s link
This provides packet and byte counters that can help identify unusual traffic increases.
Monitor Active Connections
Administrators can inspect current network connections with:
ss -s
For more detailed information:
ss -ant
A sudden increase in connections can be a useful indicator, although it does not automatically prove a DDoS attack.
Inspect Network Traffic
For controlled troubleshooting environments, packet capture tools such as tcpdump can provide deeper visibility:
sudo tcpdump -n -i eth0
Administrators should use packet captures carefully because large DDoS events can generate enormous amounts of data.
Look for Abnormal Patterns
Security teams should examine several characteristics simultaneously.
Source IP distribution
Destination ports
Protocol distribution
Packet rates
Connection rates
Geographic patterns
Request frequency
HTTP response codes
Bandwidth utilization
No single indicator reliably identifies every DDoS attack.
Rate Limiting Can Reduce Application Pressure
For web applications, rate limiting can help prevent excessive requests from consuming application resources.
A conceptual Nginx configuration might look like:
Nginx
limit_req_zone $binary_remote_addr zone=api_limit:10m rate=10r/s;
The exact configuration must be adapted to the application’s legitimate traffic patterns.
Firewalls Are Not Always Enough
A common mistake is assuming that adding firewall rules will solve a large DDoS attack.
A firewall may successfully block malicious packets while the upstream network connection remains saturated.
In that scenario, the firewall is defending the server but not solving the bandwidth problem.
This is precisely why upstream mitigation is so important for large-scale attacks.
CDN and DDoS Protection Layers
Organizations operating Internet-facing services should consider layered defenses.
Internet
↓
Upstream DDoS Protection
↓
CDN / Edge Network
↓
Load Balancer
↓
Firewall
↓
Application Servers
↓
Databases
Each layer should have a defined security responsibility.
Logging Must Survive the Attack
During a major DDoS event, logging systems can become overwhelmed.
Security teams should therefore separate critical security telemetry from ordinary application logs whenever possible.
Centralized logging and sampling can help maintain visibility without allowing attackers to consume all available storage and processing resources.
The Incident Shows Why Redundancy Matters
A resilient messaging platform needs more than redundant servers.
It needs redundant networks, providers, DNS infrastructure, monitoring systems, communication channels, and incident-response procedures.
Threema’s experience demonstrates how an apparently unrelated status-page problem can make an already difficult incident more confusing for users.
Security and Availability Are Connected
Encryption protects the confidentiality of communication.
Authentication protects identities.
Integrity controls protect messages from unauthorized modification.
DDoS defenses protect availability.
A mature security architecture needs all four.
DDoS Does Not Require Data Theft
Attackers do not need to steal information to cause significant damage.
Disrupting communication can itself be the objective.
For businesses, downtime can result in lost productivity, delayed operations, customer frustration, reputational damage, and financial costs.
Attackers Can Exploit Dependency Chains
The targeting of
Modern companies depend on layers of third-party infrastructure.
Application
↓
Hosting Provider
↓
Network Provider
↓
DNS Provider
↓
Transit Provider
↓
Internet
A weakness or attack at any layer can affect the final service.
Third-Party Risk Requires Continuous Assessment
Organizations should periodically identify which external services are critical to their operations.
The important question is not simply:
Is our application secure?
It is:
“What happens if one of the services our application depends on becomes unavailable?”
Incident Response Must Include Communication
A technical response without communication creates confusion.
Users should receive clear information about:
What happened
When it started
Which services are affected
Whether data was compromised
What users should do
When the next update will arrive
Even when the technical investigation is incomplete, communicating uncertainty honestly is better than leaving customers guessing.
DDoS Protection Should Be Tested Before an Attack
Organizations should not wait for their first major attack to discover that mitigation capacity is insufficient.
Controlled testing, tabletop exercises, traffic simulations, and provider reviews can expose weaknesses before attackers do.
Availability Should Be Measured Like Security
Organizations frequently measure vulnerabilities and patch status.
They should also measure:
Mean time to detect
Mean time to mitigate
Maximum sustainable traffic
Provider failover time
DNS recovery time
Status communication delay
Backup communication readiness
These measurements provide a much clearer picture of operational resilience.
What Undercode Say: The Bigger Lesson Behind the Threema Attack
1. Privacy Is Not the Same as Availability
Threema’s security architecture can protect communications while the service is unreachable.
That distinction is fundamental.
2. DDoS Attacks Are Operational Weapons
Modern DDoS attacks can be used to create disruption rather than steal information.
3. Changing Attack Patterns Are Increasingly Important
Attackers can continuously modify their techniques, forcing defenders to adapt dynamically.
- Infrastructure Providers Become Part of the Security Boundary
A company’s security posture cannot be evaluated independently from its critical providers.
5. The Network Edge Is a Battlefield
The earlier malicious traffic can be filtered, the less pressure reaches internal systems.
6. Bandwidth Is a Security Resource
An organization can have powerful servers and still become unavailable if its Internet connection is saturated.
7. Status Pages Are Security Infrastructure
Communication systems should be treated as part of incident response rather than as simple customer-service tools.
8. Independent Communication Channels Matter
Email, RSS, social networks, and emergency contact systems can provide alternative paths during outages.
9. Businesses Need Communication Redundancy
Organizations should never rely exclusively on one messaging platform for critical operations.
10. Threema On-Prem Demonstrates Architectural Independence
Running infrastructure independently can reduce dependency on centralized service infrastructure.
11. But On-Prem Requires Greater Responsibility
Organizations choosing self-hosting must also provide their own resilience and DDoS defenses.
12. DDoS Protection Must Be Multi-Layered
Application controls alone are rarely sufficient against very large attacks.
13. Upstream Mitigation Is Critical
Filtering traffic before it reaches the
14. Incident Duration Matters
Four hours of major downtime can be highly disruptive even without data loss.
- Intermittent Failures Can Be More Difficult Than Complete Outages
Users may repeatedly attempt to reconnect when a service appears partially operational.
16. Attack Attribution Can Be Unclear
The organization receiving malicious traffic is not necessarily the only intended target.
17. Third-Party Attacks Can Become Customer Incidents
An attack against a provider can quickly become an outage for its customers.
18. Monitoring Must Be Independent
If monitoring depends on the same infrastructure being attacked, visibility can disappear at the worst possible moment.
19. Security Teams Need Historical Baselines
Without normal traffic baselines, distinguishing attacks from legitimate traffic becomes harder.
20. Automation Is Becoming Essential
Large-scale attacks can evolve faster than manual defensive processes.
21. DDoS Defense Is a Continuous Process
Protection should not be treated as something purchased once and forgotten.
22. Cloud Does Not Eliminate DDoS Risk
Cloud infrastructure provides scalability, but attackers can also exploit scalable resources.
23. Encryption Cannot Stop Infrastructure Attacks
Strong encryption protects content but does not prevent traffic floods.
24. Availability Belongs in Security Planning
Availability should be included in threat modeling alongside confidentiality and integrity.
25. Business Continuity Should Include Messaging
Alternative communication channels should be documented before emergencies happen.
26. Customers Need Transparent Incident Reports
Clear post-incident reporting helps users understand what happened and what changed.
27. Status History Builds Trust
An incident history gives customers a transparent record of service reliability.
28. RSS Can Support Automated Operations
Administrators can integrate status feeds into monitoring and alerting systems.
29. Providers Should Test Their Incident Communication
A technically successful mitigation can still feel like a failure if customers receive no useful information.
30. Resilience Is More Than Redundant Servers
Network, DNS, providers, monitoring, communication, and operational procedures all require redundancy.
31. DDoS Attacks Can Become Reputation Attacks
Repeated outages can cause users to question whether a service is reliable enough for critical communication.
32. Attackers Benefit From Uncertainty
When users cannot determine whether an outage is local or global, confusion increases operational pressure.
- Security Teams Should Assume Attackers Will Adapt
A mitigation strategy should be designed with changing traffic patterns in mind.
34. Incident Response Needs Real-Time Feedback
Defenders must continuously evaluate whether mitigation is actually reducing malicious traffic.
35. Large Attacks Require External Partnerships
Specialized DDoS mitigation providers can offer capacity beyond what individual organizations can reasonably maintain.
36. Small Organizations Face the Same Problem
A smaller company may be even more vulnerable because it has fewer network and security resources.
37. Service Architecture Determines Blast Radius
Centralized systems can create large-scale outages, while distributed architectures may limit them.
38. Security Design Should Consider Failure Modes
The important question is not whether an attack will happen, but what happens when it does.
- DDoS Is Becoming Part of the Normal Threat Landscape
Organizations should treat denial-of-service attacks as a routine operational risk rather than an extraordinary event.
40. The Final Lesson Is Resilience
The strongest security system is not the one that never experiences an attack.
It is the one that can absorb the attack, communicate clearly, recover quickly, and emerge stronger afterward.
✅ Threema Was Hit by DDoS Attacks
The incident described is consistent with
✅ Threema On-Prem Customers Were Not Affected
The distinction is accurate because On-Prem deployments operate on customer-controlled infrastructure rather than relying on the same hosted environment affected by the incident.
✅ The Attacks Were Difficult to Mitigate
Threema reported constantly changing attack patterns and sources, which is a recognized characteristic that can complicate DDoS mitigation.
❌ A DDoS Attack Means Messages Were Stolen
There is no basis in the incident described for claiming that attackers breached Threema’s encryption or stole users’ messages. The confirmed issue was service availability.
✅ Additional DDoS Protection Was Deployed
Threema responded by adding specialized upstream DDoS protection intended to filter malicious traffic before it reached its infrastructure.
Prediction
(+1) Threema Will Strengthen Its Infrastructure Resilience
The incident is likely to accelerate investment in upstream DDoS mitigation, traffic filtering, monitoring, redundancy, and automated attack detection.
(+1) Service Transparency Will Improve
The planned incident history and RSS feed should give users and administrators better visibility into future outages and reduce uncertainty during incidents.
(+1) Businesses Will Reconsider Single-Platform Communication
Organizations using secure messengers for critical operations are likely to place greater emphasis on backup communication channels and business continuity planning.
(+1) On-Premises Options May Gain More Attention
Companies with strict availability requirements may increasingly evaluate architectures that give them greater control over infrastructure and reduce dependence on centralized service environments.
(-1) DDoS Attacks Will Not Disappear
Additional protection can reduce the impact of attacks, but it cannot eliminate the underlying threat. Attackers will continue searching for new ways to overwhelm or bypass defensive systems.
(-1) Intermittent Outages May Remain Difficult to Diagnose
Even after stronger mitigation is deployed, adaptive attacks can produce partial or regional disruptions that are harder to identify than a simple complete outage.
Final Perspective: The Attack Was a Warning, Not Just an Outage
The Real Security Battle Is Availability
The Threema incident is a useful reminder that cybersecurity does not end with encryption.
A secure communication platform must also remain reachable when someone deliberately tries to make it disappear from the Internet.
Resilience Is the Next Layer of Privacy
For privacy-focused services, trust depends on more than protecting messages. Users also need confidence that the infrastructure carrying those messages can withstand pressure.
Threema’s response, including additional upstream DDoS protection and planned improvements to its status infrastructure, shows the right direction.
The Most Important Lesson
The biggest lesson is simple: security is not only about keeping attackers out. It is also about making sure they cannot easily force everyone else offline.
As DDoS campaigns become larger, more adaptive, and more difficult to attribute, resilient infrastructure will become just as important as encryption itself. For Threema and every other communication provider, the challenge is no longer merely building a secure service.
It is building one that can stay available when the Internet becomes hostile.
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