I did a scan with AVG and it spotted a hidden system file with a random 8 character name beginning with 'a'. I deleted it and rebooted the system and another .sys file reappeared with a different random named, but again beginning with 'a'. It has happened a 3rd time now. The file is now called: "c:\WINDOWS\System32\Drivers\a7y22p0a.sys" Any help explaining where it is coming from would be greatly appreciated! Edit: not to panic. I almost by random found the answer - I have a CD emulator and the driver it uses is created on each boot with a random name beginning with 'a'. It's not an infection. Phew!