Firesheep is the Firefox extension that makes it easier to steal logins and take over social media and email accounts after users log in from a WiFi hotspot or even their own unprotected network.

Developers say they were simply hoping to shed light on the problem of not using SSL encryption for user sessions. But the temptation for people to use it for nefarious purposes is too great.

Zscaler researchers have created, and are now offering to every consumer, a free Firefox plugin called BlackSheep, which serves as a counter-measure. BlackSheep combats Firesheep by monitoring traffic and then alerting users if Firesheep is being used on the network.