From the Sophos Web site:
Removing rootkits without compromising system integrity is particularly challenging and needs to be done with care. Our free software, Sophos Anti-Rootkit, finds and removes any rootkit that is hidden on your computer.
Using Sophos Anti-Rootkit is straightforward. Whether you use its simple graphical user interface or run it from the command line you can easily detect and eliminate any rootkits on your computer.
Get more information and download it by following the link.