I work on a few different blogs in my spare time, some of which are work related - to see how and where I can get them to rank, and some are just for fun.
On one of the blogs I am more involved with, I noticed a bunch of comments posted from "Cheap Discount Drugs" so I did a little investigating and what I found shocked me.
It turns on that this "person" who laced hundreds of comments through my site appears to be trying to build links to his sites via my blog. Not only that, but I found a few (3183 to be exact) more of these bogus posts. All of them had between 1 and 4 links back to literally thousands of domains.
I use Movable Type for this particular blog so I thought (naively, before I knew how many there were) that I would simply ban the IP from posting. Well, I got to IP 38 before I realized how badly my blog had been hit over a 5 day period.