Sophos Anti-Rootkit is a portable tool that can be used to discover and remove any rootkit that may reside in a computers running processes, registry or on a local hard drive. A rootkit also known as (Root Kit) is basically a set of tools that are used to conceal a malicious program from the computer user.
DrWEB CureIt is free antivirus software. This stand alone utility can be used to quickly scan drives for viruses, and if necessary cure an infected computer.
McAfee Stinger is a free portable virus removal tool that can be stored and run entirely from a removable USB device. This utility is often used by technical users and computer administrators to help deal with and repair infected computer systems.
Avast Virus Cleaner was a Fee virus and worm removal tool that could even be installed to and launched directly from a portable USB device. It was a nice tool to have available for those extreme situations when you encounter an already infected computer.
No computer should be without Good Antivirus Software, Free & Open Source that is even better. One nice Portable Antivirus solution is ClamWin Portable.