There is a new plug-in for Firefox, called Firesheep, that allows those that have implemented it to "sidejack" some of your accounts, such as Facebook, Gmail, etc. when you are logged into a public wi-fi network. The author of this plug-in states that his intentions are not malicious but that he just released the app to show people how vulnerable they are.
Of course, it now enables everyone who installs this plug-in to now not only know what apps like Facebook others are running but allows them to log into those accounts and use them just as if they were the owner.
So what can we do about it. Well, the obvious answer is to not log into certain accounts when using public wireless networks such as libraries, MacDonald's, Starbucks, etc. These accounts include Facebook, Gmail and other similar accounts. Also, when using your wireless phone, don't connect to the public wireless network, use the 3G or 4G connection.
For a more in depth look at this and for tips on how to protect yourself, you can go to this article from CNN Tech.
Its getting really scary out there!