LAS VEGAS -- Black Hat USA -- Here's another reason not to use WiFi unprotected: Hackers can "sidejack" your machine and access your Web accounts, researchers demonstrated here last week as part of the "Simple Solutions to Complex Problems from the Lazy Hacker's Handbook." (See Black Hat: How to Hack IPS Signatures.)

Robert Graham, CEO of Errata Security, showed -- and released -- his new Hamster tool, a more powerful version of his Ferret WiFi sniffer that can grab users' Gmail, Yahoo, and other online accounts. Hamster basically clones the victim's cookies by sniffing their session IDs and controlling their Website accounts. (See Joke's on Me and Tool Uncovers Inadvertent 'Chatter'.)

"You can be in a café and see a list of people browsing [over WiFi]. And you can highjack and clone their Gmail system, for example, Graham says. "We know it's theoretically possible, so we wanted to prove it... This is very powerful because it's so easy to do."

The tool doesn't require grabbing passwords, just the cookies and URL trail the user leaves behind. "Hamster is a proxy, just like Squid" HTTP proxy software, he says. "I didn't want to use Squid because it's a bigger program and I wanted to create a small kit I can give people to download."

Hamster only runs on Windows, and Graham says the code is still a bit finicky, but it proves that attackers can not only sniff, but grab, a victim's online accounts.

Graham says Hamster doesn't let an attacker actually see the victim writing an email, but the "state information" so that the attacker can then pose as the unsuspecting victim -- and read, send, and receive email on his behalf.

"The cool thing with Ferret is that a lot these cookies are persistent, so I can copy them now, go home and load them into Hamster, and most will still work," he says.

Graham tested his tool at Black Hat last week, but he lamented that it wasn't easy to find a large number of users here who venture into WiFi unprotected. "Everyone is getting so paranoid around here."

Besides the obvious "don't use open WiFi recommendation," Graham says users should routinely log out of their Web sessions, which wipes out their cookie trail and thus dead-ends the Hamster attacker.

— Kelly Jackson Higgins, Senior Editor, Dark Reading