Akismet reports it has caught its 20 billionth spam.”an average of around 10 million per day over the 5 years since Akismet first launched.”
Akismet is a hosted web service by Automattic, the creators of WordPress.com, that saves you time by automatically detecting comment and trackback spam.
Each time a new comment, trackback, or pingback is added to your site it’s submitted to the Akismet web service which runs hundreds of tests on the comment and returns a thumbs up or thumbs down. As a result, you don’t have to waste your time sorting through and deleting spammy comments from your blog.
More info: http://akismet.com