'parasites' Stealing Commisions....

I hope I'm in the right forum. My wife is involved in putting up websites based on the affiliate marketing program. A lot of the people involved in this are certain that "parasites" are "parking" on their sites during peak traffic times and redirecting sale hits in order to steal commisions. The companies don't seem too concerned since to them a sale is made. They don't care who gets the commission. And the people like my wife aren't big players. No one seems to even know how it is being done. Any ideas on something to look for? Any ideas at all?

The best bet is probably to run a set of security scans, starting with Spybot and/or AdAware (in my sig) and then run HijackThis to copy/post the log here for experts to check out. They would have to install some kind of hijacker software on her machine for this to happen and it can be disabled if we can find it.