Just to clarify the article, the title is a bit misleading, and really should read "Spyware Floods In Through Any-Program-You-Use-To-Connect-To-The-Internet-With." It really underscores that you shouldn't be downloading or executing anything off the Internet unless you know where it came from (or are prepared to deal with the consequences).
BitTorrent works by creating a torrent file that describes how a file(s) is constructed. Users can download the torrent file, and when run with a torrent program, it will contact other torrent programs on the Internet, looking for the pieces. The torrent program will also share existing pieces that you've collected, but only for the particular torrent file (it does NOT share out your hard drive). Torrents work well in distributing information quickly as multiple sources can give you several pieces simultaneously. You don't need to obtain the file from a single source one piece at a time if you were downloading it via HTTP or FTP.
In this case Direct Revenue is creating torrents of files that users want that include their spyware program IN ADDITION TO the original file. They are not co-opting the original file or infecting torrents that are not their own. In fact there is some legality on their repackaging and distributing these torrents.
If you download a torrent distribution file for a Linux boot disk from Knoppix.org then there is no way for Direct Revenue to add their spyware into that torrent. If you download a torrent distribution file for the same Linux boot disk from Direct Revenue then there is NO guarantee that you won't have an unwelcome hitch-hiker added to your download. Even then, once their spyware is downloaded to your machine you will need to execute it for the spyware to sink its hooks into your system.
Frankly, anyone who obtains (for example) boot disk.ISO and an executable file they don't why it's there, and decides to run the executable, deserves to be thoroughly chastised with the same tone of voice reserved for people who cross the street without looking both ways.
Slashdot has a good discussion about this here:
http://yro.slashdot.org/article.pl?sid=05/06/16/1558229&tid=158&tid=...