Grumble Grumble Grumble
You did burn backup copies of all of those video files, right????
Get one of those utilities that recalculates the file CRC32 checksum of your video files. The original torrent link page of the group hosting the tracker will usually have the CRC checksum value posted along with the torrent link, or its included as a part of the file name. If the checksums don't match, it means that the virus/trojan has maliciously modified your video files to something unusable... (tough luck!)
(heres a simple CRC/checksum utility for windows... QuickSFV - Reviews and free QuickSFV downloads at Download.com )