MRT.exe, if you run it explicitly (say download it
after the second Tuesday from Microsoft instead of
getting it from Windows Update) during its scan
reports 4 infected files, but at the end reports
no files infected.
Apparently it does this on any XP machine.
I'd guess some standard files match the virus
pattern and they ignore those matches at the end.
It's a little quick but it seems to be in the
JavaScript general area of quick scan.
--
On the internet, nobody knows you're a jerk.