From a Basecamp blog post, in a lull from the denial-of-service attack earlier today:

Criminals attacked the Basecamp network with a distributed denial-of-service attack (DDoS) attack this morning. The attackers tried to extort us for money to make it stop. We refused to give in and worked with our network providers to mitigate the attack the best we could. Then, about two hours after the attack started, it suddenly stopped.

We’ve been in contact with multiple other victims of the same group, and unfortunately the pattern in those cases were one of on/off attacks. So while things are currently back to normal for almost everyone (a few lingering network quarantine issues remain, but should be cleared up shortly), there’s no guarantee that the attack will not resume.

So for the time being we remain on high alert. We’re collaborating with the other victims of the same group and with law enforcement. These criminals are sophisticated and well-armed.

This really sucks.