Firesheep a Firefox addon has recently become very popular for easily carrying out a HTTP session hijacking attack. Http session hijacking attack can't be considered as a very sophisticated attack but needs some technical knowlegde to be performed . But Firesheep makes the attack a child's play. Firesheep was developed by Eric butler for Firefox, it was released at Toorcon 12 to demonstrate how serious cookie stealing can be.
Now lets understand how Firesheep actually works. When you provide your username and password in login forms of different website and submit it, the browser first encrypts the password and then sends it over the network. The corresponding website compares the information against its internal database and if they match, it sends a cookie(a small text file) to your browser. The browser saves this cookie and uses it to authenticate the user on the website every time the user opens a different page of the website. When the user logs out of his account the browser just deletes the cookie. Now the problem is that this cookies are not encrypted before sending over the network, due to this a hacker can capture this cookies and using them authenticate himself as the user from whom the cookie was stolen.
Now lets see how to use Firesheep.


1) First download and install WinPcap (WinPcap in Windows is used for capturing network traffic.) You can use Pcap in libPcap library for unix like systems.
DOWNLOAD WinPcap

2) Download and open Firesheep in Firefox, it will automatically install it. Or just drag it and place it over Firefox shortcut (Firesheep at this instant is not supporting Firefox 4 ).
DOWNLOAD Firesheep

3) After it is installed a side bar will appear in the browser with a button "start capturing", press it and sit back. In few seconds you will see account details with photos of the target. Click on one of it and you will directly enter in his account. Simple as that.

Note:- Using Firesheep to hijack others account is illegal under wiretapping Act.