fthiess writes "Comment spam is in many ways even more annoying than regular email spam, since you generally have to do more than just hit the delete button to get rid of it. Its defining characteristic is that spammers abuse websites where the public can add content (blogs, wikis, forums, and even top referrer lists) to increase their own ranking in search engines. It seems, however, that the days of content spam are numbered: today Google announced that, in partnership with MSN Search and Yahoo!, that they have implemented a way to block content spam."
"Briefly, you just change your blogging/wiki/forum/etc. software so that any hyperlinks in publicly-contributed text have a new rel=nofollow attribute added to any anchor tags. Google, MSN, and Yahoo! will now no longer index any such links, so the motive for content spamming disappears. Especially hopeful is the fact that a slew of makers of blogging software, including Six Apart, have announced they are supporting the new attribute."