Suppressing Comment Spam
Google has added support for suppressing comment spam. Comment spam consists of URL's and keywords tossed into blog comments for the sole purpose of gaming search engine rankings. Increasingly, comment spammers are using bots to splat out these sorts of "comments".
Google's spider now supports a "nofollow" attribute value to separate blog postings from comments. It tells the spider to ignore hyperlinks appearing within comments, trackbacks and referrer lists. Interestingly, the "nofollow" attribute value was already part of the HTML DTD, but this represents a new use.
Google, in a recent blog post, said its spider has already begun recognizing the tag. Consider the old tag:
Visit my <a href="http://www.example.com/">fake Rolex</a> site
That comment would be transformed to
Visit my <a href="http://www.example.com/" rel="nofollow">fake Rolex</a> site
Search Engines, Bloggers Team to Fight Spam