Looks like the debian developement server (hosting the cvs amongst other services) has been compromised. The Debian folks are still investigating the incidents at this point. No words on whether the any source code were altered yet.

From stories like these, we can't stress the point of having a HIDS system. From experience, some server could be compromised over 6 months before someone even notice about it. Having some type of HIDS such as AIDE or Tripwire can hopefully reduce the detection time.