Wow that was fast, though I don't suppose I should be surprised. Earlier this evening I visited the blog of a colleague of mine and saw in a post of his (thanks M3!) that leaked Windows 7 RC files that were obtained through bittorrent have been found to have been infected with a trojan. I say that I shouldn't be surprised because in research we supported a couple off years ago we discovered that the typical methods that someone would use to find and obtain unlicensed software (much of it over bittorrent) exposed users to significant risk from trojans and other malware.
Not that I have anything against bittorrent. In fact I invited Bram Cohen, creator of Bittorrent and it's protocol, out to Microsoft a few years ago to have an informal conversation about the relationship of the Internet and technology such as Bittorrent to software piracy. As I recall it was a good conversation and I certainly respect him and the technology as innovative and powerful.
I do hope that no one has had any problems as a result of the infected files. This example unfortunately shows that there are those out there who see the significant interest in something such as Windows 7 as an opportunity to try to take advantage of others. In the end this is the same motivation as those who create and sell counterfeit software, to fool users or customers for the purpose of taking advantage of them. When getting something that is free or should be paid for it really is best to go to the source or through authorized distribution to avoid the risks of this kind of thing.