You will instantly understand why this feature is important when I tell you that the original name of Twitter was "Friendstalker". In fun. I think. But it's clear that if there is some weirdo out there on the Net who has an unhealthy interest in your life and doings, then it can be a creepy or even downright scary thing to realize that they are subscribed to your updates.

Now, to be fair, you never really know who is reading your blog, skimming your Facebook profile or following your Twitter updates, so at some level if you decide to open yourself up to more public scrutiny by sending out geolocation and other updates then it's hard to say that only nice people should follow you. Yes, you can have a private Twitter update and only allow known friends and family to follow you, but it's like the question of absolute security for online data: if it's online, it cannot be absolutely secure.

Back to Twitter, though. If you want to block someone from following you in Twitter, you need to not be following them but have them following you (after all, why would you follow someone who was a creep or psycho? :-). Then click on your "Followers" link and find them or just go straight to their Twitter profile page.

In the former case you'll see something like this:

and in the latter case, something more like this:

Either way, click on "block" and you'll see this:

If you really want to block that person, as detailed above, then simply click on "OKAY, I STILL WANT TO BLOCK THIS PERSON" or, if you've had a change of heart (as I certainly have with Brian Solis), click on "Nah, never mind, we're cool"