We are seeing vast numbers of sites being compromised at the moment.
These sites are using an older version of AWStats, which is a free tool that generates advanced graphical statistics for web, ftp or mail servers.
There is a vulnerability in AWStats 6.2 and previous versions which leads to remote command execution. This gives an attacker almost full control over the server.
This vulnerability was first disclosed on 17th January 2005. It has been fixed in AWStats 6.3, so we urge everybody who is using AWStats to make sure they are using 6.3.
Although we are seeing mostly defacements, you are highly recommended to thoroughly check your servers if you have been running AWStats 6.1 since 17th January.