Firesheep is a Firefox extension used to hijack web sessions, usually used over WiFi networks. Firesheep doesn't steal usernames and passwords, instead it copies session cookies used on authenticated websites. These are then used to impersonate the hijacked connection. Session hijacking, or sidejacking is a well known problem, ranking 3rd on OWASP's (Open Web Application Security Project) Top 10 Application Security Risk list. Attackers using Firesheep just need access to network traffic -- such
Lots of information is carried in HTTP headers -- more than enough to get attackers started. Unless you are using an encryption method like SSL/TLS end to end, this information is available to anyone with access to the media.
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