Corruption detection only detects differences from the source(s) - it will not detect viruses, trojans, worms or the like.

It is very unlikely that audio files will contain a virus. It isn't impossible - but such a virus would probably only work on one specific player and are generally very limited in what they can do.

The worst that you are likely to experience from a corrupt file is a square wave in the audio (very sharp and hard rises and falls in the waveform when it reaches the speakers). But it isn't particularly likely in a corrupt MP3s and poorly ripped audio (clicks and pops) are at least as bad. This sort of thing can, theoretically, cause damage to your speakers (more so if at extreme volume and repeated frequently). But don't worry about - there are much easier ways to destroy your speakers.

The fact that you are picking up a high percentage of corrupt files suggests that someone has modified their files - it might be something as trivial as changing the ID3 tag.

Mark

P.S. The check for file corruption is a recent addition to LimeWire - this is why people haven't seen it previously.