Malware on GNU/Linux
[M]alware includes not just virii, but worms, trojans and root-kits. These known and widely available tools are not the only options available to intruders either.
GNU/Linux users should not have any false sense of security just based on the fact that viruses designed for exclusively for windows won't run on GNU/Linux.
Here is a list of "Linux computer viruses" according to a page on wikipedia.org.
The following excerpt lists various kinds of malware, not just virii...