John, I've used aswMBR, rkill, RootkitBuster, and Sophos Virus Removal Tool at various times just as second opinion on-demand scanners. Sophos is slow and doesn't give any indication of how far along the scan is. It leaves the user guessing if the scan will finish in 10 minutes, half an hour, or something else. The others just chug along and apparently do their thing.
I have a clean system. To the best of my knowledge I've never been infected. So all of the scanners give a "0 threats found" mesage. Does that mean my computer is really clean, or does it mean the scanner just didn't find something that was deeply hidden?