Also be aware that some viruses and malware copy themselves into your system restore shit, so that you run a virus check, it deletes them, and then unbeknown to you next time you reboot they restore themselves. The common place for them to lurk is the in System Volume Information folder on c:\ - however unless you've got your settings right you won't be able to see or access this folder on your machine.....there's plenty of info on this via google.