A new version of the Carberp Trojan attempts to steal money from Facebook users by duping them into divulging an e-cash voucher, researchers say.

"Carberp replaces any Facebook page the user navigates to with a fake page notifying the victim that his/her Facebook account is 'temporarily locked,'" says Trusteer CTO Amit Klein in his blog. "The page asks the user for their first name, last name, email, date of birth, password, and a Ukash 20 euro [approximately $25 U.S.] voucher number to 'confirm verification' of their identity and unlock the account.

"The page claims the cash voucher will be 'added to the user's main Facebook account balance,' which is obviously not the case," Klein states. "Instead, the voucher number is transferred to the Carberp bot master, who presumably uses it as a cash equivalent, thus effectively defrauding the user of $25."

The emerging man-in-the-browser (MitB) attack exploits the trust users have in Facebook and the anonymity of Ukash e-cash vouchers, Klein writes. "Unlike attacks against online banking applications that require transferring money to another account--which creates an auditable trail--this new Carberp attack allows fraudsters to use or sell the e-cash vouchers immediately, anywhere they are accepted on the Internet."

This type of attack is likely to grow as e-cash becomes more frequently used, Klein warns. "Like card-not-present fraud, where cybercriminals use stolen debit and credit card information to make illegal online purchases without the risk of being caught, e-cash fraud is a low-risk form of crime," he said. "With e-cash, however, it is the accountholder, not the financial institution, who assumes the liability for fraudulent transactions."

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