Sorcha earlier today I happened across this page - PestScan - on Zone Alarm's website.
It is a scan which you can run online if you use Internet Explorer. It tells you what nasties or questionable items it finds, and gives instructions about how to remove specific problems manually. It is essentially a taster for their product you purchase which will remove stuff automatically.
It might be worth using to check your system. I've not had time to play with it yet, so can't give any indication of how useful the removal instructions are.
Quack!
GtD.