Servers hosting the GNU/Linux source code for the Debian project have been compromised, and project leads are advising developers to place close attention to their checksums. While it isn't certain that source code has been tampered with, the intrusion has caused the delay to a point release of the distro, release 3.0r2.
Machines hosting the bug tracking system, mailing list, and source code tree were affected. You can find the latest on the security breach here.
At publication time, Debian was not accepting new packages and didn't expect normal service to be resumed until Wednesday. ®