1st of all, this could be any # of things....
1) When you use the internet, are you using a firewal ? Many people here will tell you howImportant it is to use one.
2) Do you have a good Anti-Virus on your computer? and does it have all the Definitions up to date?
3) When you do a fresh install of Windows, Are you going straight to Microsoft for ALL CRITICAL UPDATES.
(you don't have to update to SP2 if you don't want to)
4) Do you have at least 2 good Spyware programs on your comp. protecting it....(I prefer Spybot Search & destroy) (also Ad-aware personal edition)
5) and last but not least....Check the Run & Run once folder, once in a while in the registry.
HKEY_LOCAL_MACHINE --> SOFTWARE --> MICROSOFT --> WINDOWS --> RUN
to get there click start/run/ type regedit & hit enter.
" Let the music move you "