The attack is actually quite simple. First job is to be able to sniff data packets and like open Wi-Fi network or any other open network. Download Ferret to copy all the cookies flying through the air. Finally, those cookies are cloned into browser – in easy point-and-click fashion – with a home-grown tool called Hamster.This story has been elaborated by Graham here
The attack can hijack sessions in almost any cookie-based web application and Graham has tested it successfully against popular webmail programs like Google’s Gmail, Microsoft’s Hotmail and Yahoo Mail. He stressed that since the program just uses cookies, he only needs an IP address and usernames and passwords aren’t required.
He has also included a slideshow here:Gmail hacking at Blackhat
If you want to prevent your accounts from being hacked then force https throughout a gmail session.Change your http://mail.google.com bookmark to https://mail.google.com. Or type in the full URL in your browser starting with https://, or else your browser will assume http:To ensure that your entire gmail session uses https, grab the GmailSecure greasemonkey script:
