Antibot is a free wordpress plugin that blocks all kinds of bad bots crawling your website.
Block spam referrals showing in Google Analytics and save bandwidth. Central database of sites, ability to add custom URL's and stats.
The most advanced protection against sploggers and spam users registration, is fully WordPress,WordPress MU ,BuddyPress and bbPress 2.0 compatible
Stop the Spam bot as semalt and buttons-for-website that appear on Google Analytics and have real reports.