Twitblock is a free service that will analyze your follower list to help you determine who’s real and who is a spambot.  By scoring accounts using a Bayesian filter, it filters all of the accounts that follow you and assign them a score. The higher the score, the more likely they are to be fake.  Twitblock will give you three choices for each potential junk account ranked 60% or higher: Not Spam, Block or Report.

Why block junk users?  Blocked users will not be able to add your Twitter account to their lists, have their @replies or mentions show in your mentions tab, be able to follow you or see your profile picture.  Twitblock can also show you who you have block already, something you cannot do on Twitter.  If you are not bothered by spam on Twitter, then you probably don’t need this app, but if you don’t want spam accounts operating in your social networks, give it a try!  You can also manage the people you follow, your Twitter lists and your current blocks.