When I first installed broadband, the installer told me to disable any real-time virus software, so I did (I used Norton then). The installer connected me to the net early in the installation, and before it closed and I could reactivate Norton, I was hit by a blaster worm. It damaged 50 windows system files (not to mention 200 other files) which were left corrupted after Norton ‘repaired’ them. Lousy Norton…
I had to format and do a clean install.