Servers belonging to the open source Debian Project, which makes a version of the Linux operating system, were hacked last week, according to statements posted by project organisers on the group's website and to a European CERT (Computer Emergency Response Team) site.

Four servers that host the project's bug tracking system, mailing lists and various Web pages were compromised on Thursday. However, the intrusions do not affect a software update for the Debian Linux operating system, which was released Friday, according to statements from Debian.

The intrusions forced the Group to suspend e-mail service for developers through the debian.org domain and lock user accounts on other machines used by project developers as a precaution, according to information posted on the Web site of project member Wichert Akkerman.

Content from compromised servers was verified using server log files and digital signatures and moved to different machines, according to information on Akkerman's site.

Debian Project developers were told to assume that their passwords to debian.org were compromised. Access to debian.org machines would be locked until Project members have cleaned all affected machines, Akkerman's site said.

Project members were also told to check for intrusions on any machine that they logged on to from a debian.org machine, update user and administrator passwords on those machines and get new SSH (Secure Shell) keys for conducting secure communications between machines, according to a post on Akkerman's Web site.

Despite the intrusions, a new point release for Debian GNU/Linux 3.0, release 3.0r2, was not affected by the compromise and is safe to install. The release contains security updates and bug fixes to the most recent release, according to Debian.

Debian is a free version of the Linux operating system that combines an operating system built on the Linux kernel with software tools from the GNU project, another open source software project. The software is maintained by a worldwide community of volunteer developers and donations of money, services and equipment.

This is just the latest security breach of a well-known open source software group. In August, the Free Software Foundation, sponsors of the GNU free software project, said that a server housing the group's Linux software was broken into by a malicious hacker.

In that attack, intruders compromised an FTP (File Transfer Protocol) server that housed software making up the core of the Free Software Foundation's GNU/Linux operating system, including the GNU C language library and compiler, as well as other software utilities.

Complete cleanup of the machines following the intrusion will take until Wednesday, after which the Debian Project would provide more details about the compromise and steps it was taking to prevent future intrusions, according to information on Akkerman's Web site.