Rootkits are a special flavor of malware that is designed to hide itself from not only antivirus programs, but from the OS itself. They can be tricky to detect and harder to get rid of.
Two free tools are available that will help you detect rootkits on your Windows system:
- Panda Anti-Rootkit (www.pandasoftware.com)
- AVG Anti-Rootkit (www.grisoft.com) (no longer being updated – functionality rolled into their commercial 8.0 anti-virus product)
- Sophos Anti-Rootkit (www.sophos.com)
- McAfee Rootkit Detective (www.mcafee.com)
Panda, AVG, McAfee, and Sophos are established and well respected anti-malware companies that have been in business for many years.
Both of these tools operate much like traditional virus scanning tools, in that you manually invoke the tool and select which hard drives you wish to scan.