This isn't a virus, its a rootkit (something manually installed by an attacker
after they've already compromised your box by other means). A virus is a program that automatically self-replicates between systems, in the process compromising them.
http://www.trendmicro.com/vinfo/viru...%5FHACKTOP%2EA
http://en.wikipedia.org/wiki/Rootkit
Anyway definitions aside you should do the following:
1) Disconnect your machine from the internet
2) Boot off a LiveCD (Knoppix, PCLinuxOS, your distro's install CD in rescue mode)
3) Run chkrootkit, rkhunter or a similar rootkit hunter (Knoppix has chkrootkit I think) to make sure the TrendMicro warning isn't a false positive
3b (optional) ) Look through the logs of the infected install and try and see how the attacker got in. Especially look through /var/log/messages and apache logs. Do you run something with known vulnerabilities like phpBB on a webserver? What version of what distro are you using? Do you keep up with security updates?
4) If the the rootkit is confirmed backup your user data (important stuff in /home, /var and /etc) and reinstall Linux.