Sophos' free Virus Removal Tool ran for several hours and finally stalled at the following point - Scanning item: PHYSICAL:081:0000:0000:0001 - Threats found 0. After leaving it in this state for a few hours I rebooted.
On reboot, it also seems to have caused some interference in Windows Security's ability to detect that Norton Antivirus is installed.
Win Vista, 750GB, HPM8430F, Norton 360
This thread was automatically locked due to age.