Holy fucking shit! What the fuck were the people on that computer doing!?
Not too much of a mystery. The nasty bug they picked up had set their machine up as a rogue file-sharing machine. Or file-sharingrogue files. Whatever you want to call it.
There were directories upon directories containing files (mostly identically-sized, but with some variations) themed around popular download terms, like "Microsoft Office 2007", with expansions along the lines of "Microsoft Office 2007 !!GeNuIne EdItIoN!! [CRACKED]". Almost certainly one single nasty download had created all of these (mostly copying, perhaps padding some out or using a basic polymorphic system to change the file signature in other ways, but all with minimum effort), as it would have almost certainly done on many other machines, maybe in the manner of a botnet. Then it would get the machine communicating with various P2P sites and wait for other people to try to get the bait-files. Which are themselves instances of either this machine's primary infection or some other kind of malware that the people behind it want spreading.
A simple, if diabolical, idea. If done on enough machines, a single machine wouldn't have to send out much P2P traffic to seed the rogue file-shared files, meaning that it'd stay under the radar by not swamping the connection of any particular household/ISP already embracing/accepting a degree of P2P network usage, plus the rogue files would appear near the top of most people's search-lists as an item with a decent degree of availability.
edit: Forgot to say, I'm not worried about the above inspiring anyone, as it's a pretty obvious mechanism. I have a few ideas on how the above could be improved (e.g. to be less resource-intensive, so easier to hide), but I wouldn't want to make these public because although there's probably something like them in circulation now I wouldn't want to make it easier for those who haven't thought of them yet.