It could be misnamed files also, as they are very common and some sicko's get off on doing this...
I would suggest doing a full system scan with your Anti-Virus and your Spy-ware apps though...
Check files with Bitzi in the future...
How to use Bitzi Web Lookup .. & How to use Magnet Links & Direct Connect/Browse/Chat
Here's some good freebies....
Anti-virus:
avast! AVG free Avira Antivir Antispyware etc: ad-ware __(FREE) Spybot - Search & Destroy __(FREE) AVG Antispyware (formerly Ewido)