The core weakness discovered by by Vincent Toubiana and Vincent Verdot lies with what is called a Session ID (SID) cookie, used to identify a user to each service they access while logged in to one of Google's services.

Every time the user accesses an application, the same SID cookie is sent in the clear, which the Firesheep captures from the data sent to and from a PC connected to a non-encrypted public Wi-Fi hotspot.

Because many of Google's services use HTTPS (Gmail for instance), the attacker has to find a way to get the user to resend this SID. The most direct method is to set up a rogue access point and then use an iFrame to direct the user to a Google service (such as Alerts) that doesn't use an encrypted channel.

The attack also requires that the user has Google Web History tracking turned on. This is the system that keeps tabs of a user's search history and many people are not even aware exists because it is set as during Google's account setup procedure.

Testing the technique against 10 volunteers, the researchers were able to retrieve up to 82 percent of the links visited by them during the test period.