You probably know about social networking sites like MySpace and Facebook and blogging services like Blogger.com and WordPress but have you heard of microblogging?

Services like Twitter and Plurk let people post very short messages (140 characters or less) to their friends and acquaintances. Founded in 2006, Twitter has attracted millions of users who keep people posted about what they’re doing and thinking. It can be as simple as “I’m standing in line at the grocery store” to as profound as a quick comment about a political candidate, a world event or a new book. There’s even a video spin-off of this concept called 12 Seconds that allows people to post video clips no longer than 12 seconds.

These sites aren’t nearly as popular with teens as MySpace and Facebook. Twitter says it’s only for people 18 and up — but it doesn’t ask your age when you set up an account. Plurk is aimed at people 13 and up.

While there is nothing inherently dangerous in the sites themselves, there is the risk that teens could use microblogs to reveal personal information or engage in a relationship with someone whose intentions are less than honorable. And like any other form of communication, the door is open for a teen to take risks such as talking about sex with strangers (albeit in relatively short bursts) or getting together with someone they meet through a microblog.

By default, Twitter messages can be seen by anyone, so if you want privacy you need to go into Settings and click “Protect my updates” to make sure only people you approve can see what you type. Otherwise anyone can “follow” you and see what you enter. You can always see a list of your followers and block anyone you wish. Likewise, you can only see posts from people you follow and can search for these people by name or location.

In some ways, microblogs are like chat rooms. What you type is posted instantaneously and it can be seen by anyone. But it also lingers so people can see it later, even when you’re offline — so always use common sense.

I use Twitter but, as with any public forum, I only post information that I’m comfortable anyone knowing. Click here to follow me (twitter.com/larrymagid) on Twitter.