Threema messaging service hit by large-scale DDoS attacks

Threema, the Swiss-based secure messaging service, experienced significant service disruptions due to multiple large-scale Distributed Denial of Service (DDoS) attacks. The outages began on a Tuesday evening, causing the service to be unavailable for approximately four hours, followed by intermittent disruptions through Wednesday morning.

The company initially attributed the issues to a network problem at its colocation provider but later confirmed that both Threema and its colocation partner, Nine, were targeted by DDoS attacks. The attackers utilized changing patterns and multiple sources, which complicated mitigation efforts.

While standard users faced communication issues, organizations utilizing Threema On-Prem were unaffected because their deployments operate on independent infrastructure. Normal operations were reported as restored by 12:23 p.m. CEST on Wednesday.