Yes, I have formatted my USB drives. I just plugging them in, deleted the files which Avira complained about, then immediately right-clicked on the drive's icon in My Computer and selected format (I didn't even open or navigate inside).
My computer seems to be running normally now I guess, and AntiVir isn't detecting any more viruses. I have just scanned and attached a HijackThis log in case just to confirm my system is ok.
So any news on why I have a Y: drive appearing? When I installed MalwareBytes AntiMalware, I could scan a Y: drive (which I had never seen before), and it is the only scanning program I've used so far that allows this. But the drive icon didn't appear in My Computer then. It only appeared after I used ComboFix.
Anyway, it doesn't seem to be causing trouble I think, so I don't mind leaving it there if it's harmless.
Thank you so much for all your time and help. I greatly appreciate everything.
Next, is there a reason why you have not updated to Service Pack 2? Or now 3?
It is crucial to update to Service Pack 2, it is probably the most important update the Microsoft has ever put out for WinXP and you are extremely vulnerable without it, Service Pack 2 significantly increases the security on your computer. I recommend that you do this update as soon as possible.
Please update your computer then post back with how it went. If you have any problems please post back with as much detail as you can. This is needed because any problems updating to SP2 could indicate that there is still some infection on your system that we need to address.