Do you have the source for VFPClean so you can see what it's doing? Maybe that would give a clue as to exactly what it's doing, and why it might stop working (or need to be done again) after a while.

>What bothers me is that I can find no MSDN reference for that function.

All the more reason to do a virus scan. You might also want to run a spyware detector as well - that c&*p is getting more invasive every day. A client recently got hit by a "drive-by" installation of "NewDotNet", which is software that "allows" users to get to "custom" top level domains that are "sold" to advertisers. It works by hooking into the DNS resolution process. On this client's machine it caused any secure sites (https) to be not accessible, Windows Update wouldn't work, etc. A real pain even to detect. Their own "uninstallation" doesn't work. I ended up having to do a reinstallation of XP to get rid of it.