An article in the September issue of Wired: Spam + Blogs =Trouble answers the question "why do I have to type 'zvtmzu' to post a comment on your blog?!"
Because of splogs & link farms. Blech.
Jon Gordon on Future Tense interviewed Charles C. Mann, the author of the Wired article. Listen to the podcast or read the article (or both) to find out about this creepy world of creating faux blogs & links to generate advertising revenue.
Interesting side note: I read this article a few weeks ago when my print copy of Wired appeared in my mailbox; the article didn't go onto Wired's web site until Sept. 5. Good way for Wired to keep some mystery & $$ but also make the article available for free -- after some time passed.