it's possible only in wi-fi networks and you can stop your account getting hacked.

STEP 1:(how to hack)

1.Download firesheep Firefox extension.This is a freeware extension for firefox browser. 

 

2.  Once installed it will open a sidebar window into your firefox browser.

 

3.Now it will show all the people who are connected to unsecured wifi network.Once they login into your facebook or twitter account you will get a notification and with a single click you can login into their account.

 

this whole trick called cookie hijacking..

 

STEP 2:(how to prevent) 

simply doing https:// you can prevent your facebook account from hacked. 

 

click link below to see how to prevent it.. 

 

 http://thingss-to-know.blogspot.com/2012/01/how-to-stop-facebook-account-hacking.html

Facebook has changed our settings and said nothing about it (again). Take a look at your URL (top box on your screen.)
If you see "www" (or http), instead of "https" ... now, you DO NOT have a secure session & can be hacked.
It appears that FB went straight on line to the world wide web now.

1)Go to the drop down from where you log out: Account Settings




2)Click Security on the left top corner.


3)click Edit next to Secure Browsing.Check box, click Save.




FB has automatically set it on the non-secure setting! No wonder so many people's accounts were hacked into last week!!!!