I've been using Twitter for ages now, and this is pretty typical. I get new followers at a rate of about one a day, and most of those unfollow again after a week or so. Some broad categories of people who might follow you:
1) actual friends and people who care what you have to say
2) webcam services (usually easy to spot because the profile pictures have few clothes on)
3) other scammers/spammers, hoping you'll follow them back out of a sense of social obligation - they tweet spam on a regular basis and if you follow them, that spam goes into your Twitter feed. I hadn't heard about them trying to steal your password, but I guess it's possible.
4) businesses (both national chains and local stores) - if you include the business Twitter handle in a tweet, you may get auto-followed back. When they follow you, they can send messages @you but you won't see them unless you go into your "connect" menu. This is actually kind of nice sometimes - I ranted about AT&T and was contacted by an AT&T customer service rep within a few hours. Also, some businesses will auto-follow you based on keywords in your tweets - if you tweet about batteries, Rayovac will auto-follow you and try to send you coupons.