Hi Rainbow, Virus', spyware, trojans, etc. can all be rather insidious, sometimes they leave behind little buggy bits that will reinfect your computer later. This can mean that even though you scanned everything and it looked clean yesterday (or whenever in the past), that doesn't mean they are not back today, ESPECIALLY Trojan horses. Sometimes every time you connect to the internet you will get reinfected again, or sometimes only when you run a certain program, or type a certain key, and WHAM O, you are infected again.
One thing that might help you is not to use Internet Explorer, evil bugs love it! Firefox is a bit better. One of my computers is infected with something that only causes issue if I run IE, so I just stay away from it
I'm sorry it's not great news.... and my only suggestion for fixes is just to keep running every kind of security software you can find. I use AVG, they have a free version (
www.AVG.com) but I upgraded to the paid one, just to get more features.
Good Luck!!!!
P.S. If you can get someone to scan your computer from outside your computer (either through
www.symantec.com - though I think they offer it as a service with a fee now, or someone like DM, or a computer repair shop), you might have better luck killing your bug