Preventing comment spam
"If you're a blogger (or a blog reader), you're painfully familiar with people who try to raise their own websites' search engine rankings by submitting linked blog comments like "Visit my discount pharmaceuticals site." This is called comment spam, we don't like it either, and we've been testing a new tag that blocks it. From now on, when Google sees the attribute (rel="nofollow") on hyperlinks, those links won't get any credit when we rank websites in our search results. This isn't a negative vote for the site where the comment was posted; it's just a way to make sure that spammers get no benefit from abusing public areas like blog comments, trackbacks, and referrer lists."
Movable Type Publishing Platform: Movable Type 'nofollow' plugin
Yahoo! Search blog: A Defense Against Comment Spam
Six Log: Support for nofollow
Posted by Martin Sewell at January 20, 2005 12:30 PM