At Twitter, we see spamming as a variety of different behaviors that range from insidious to annoying. Posting harmful links to phishing or malware sites, repeatedly posting duplicate tweets, and aggressively following and un-following accounts to attract attention are just a few examples of spam on Twitter. Like it or not, as the system becomes more popular, more and more spammers will try to do their thing. We’re constantly battling against spam to improve the Twitter experience and we're happy to report that it's working.
I have noticed a good number of spam followers are nuked well before I get to check the profile.