What's happening is that these folks are following you, so you're automatically following them back. Well, not YOU, but your Twitter settings.

The problem with this is that those settings could be in your basic Twitter profile OR in some other device or app you've synced with Twitter.

Check your Twitter settings in your actual profile on Twitter itself by clicking on the little gear icon in the header (to the right of the search box) and selecting "settings." First, check and see if you have any "widgets." Then select the "apps" menu item and see which apps you've given permission to access your profile, like Facebook or TweetDeck.

Once you know which apps are attached to your profile, you may be able to turn off "automatic follow-back" in the app directly, or else just revoke access right there in your Twitter profile.

helpfully,
Bright

But it was twitter that was allowing itself to follow random people. Weird. Thanks.

It's so rare that I get to sound like I know what I'm talking about with any geekery that it was quite enjoyable.

conspiratorially,
Bright