What happened
Encrypted messaging service Threema experienced significant service disruptions after a sustained distributed denial-of-service attack hit both its own infrastructure and that of its colocation partner, Nine. The attacks struck Tuesday evening around 6 p.m. UTC and continued into Wednesday morning, leaving the service temporarily unavailable or only partially working for stretches across roughly two days. Threema said the attack was unusually hard to defend against because the traffic kept shifting: the threat actor continually changed its tactics to circumvent mitigation measures, the company said, as its team worked to filter the flood of traffic. No group has claimed responsibility, and Threema said it isn't clear whether it was the specific target or one of several targets hit at once. Users in Switzerland, India and China reported delayed or failed message delivery during the outage; business customers using Threema's on-premises version, which runs on their own servers rather than Threema's cloud, were unaffected.
Why it matters for your business
Most small businesses don't run their own messaging infrastructure, they rely on a single third-party platform, whether that's Slack, Teams, WhatsApp or Threema, and trust it to just work. This incident is a reminder that even a well-regarded, security-focused provider can be knocked offline by an attacker who doesn't need to breach anything, just flood it with traffic. If your team, vendors or customers coordinate primarily through one chat app, a similar outage would leave you without a way to reach people at short notice. It's worth knowing what your fallback communication channel is before you need one, whether that's phone, email or a second messaging app.
What to do
Identify a backup communication method your team can switch to if your primary chat or messaging platform goes down, and make sure key contacts, like clients or vendors you coordinate with urgently, have your phone number or email as well as your usual chat handle.