Have you scanned your system over with Norton AV? Also check online AV tests here WARNING: Viruses on network you should be aware of! (click on link). Whilst the problem might not be a virus, it is best to be sure. And remember not all AV programs pick up all viruses.

I'd suggest deleting that file if possible. Incomplete Download File won't delete at all (click on link). It might also be worth a reinstall of windows.

Hopefully some will have better ideas since I am not a windows expert. (or any kind for that matter)