In a case documented by San Diego-based Web security company Websense, the attack occurs after a user visits a Web site containing code that exploits a known flaw in Microsoft's Internet Explorer Web browser. The flaw is used to download and run a malicious program that in turn downloads an application that encrypts files on the victim's PC and mapped network drives, according to Websense. The program then drops a ransom note.
Even though this type of attack is not widespread at this point, Internet users should be aware of the threat, said Oliver Friedrichs, a senior manager at Symantec Security Response. "It is certainly concerning. This is the first time that we have seen cryptography used in this type of attack to hold your information hostage," he said.
"I would see this as the equivalent of somebody coming into your house, putting your valuables in a safe and not telling you the combination," Friedrichs said.
Researchers at Symantec have seen the malicious program used in the ransom attack. The "Trojan.Pgpcoder" searches a victim's hard disk drive for 15 common file types, including images and Microsoft Office file types. It then encrypts the files, removes the originals and drops a note asking $200 for the encryption key, Friedrichs said.
A Websense customer fell victim to the attack. Luckily, in this case the encryption wasn't very sophisticated and Websense was able to decode the customer's files, said Dan Hubbard, senior director of security and research at Websense. "In this case we could help, but every variant can be different," he said.
Attackers could use e-mail, a Web site, or other means to distribute the Trojan.Pgpcoder and launch a widespread extortion campaign, Symantec's Friedrichs said.
Websense, however, doesn't see a trend yet. Attackers leave a trail if they ask for money, Hubbard said: "This type of attack is not that difficult to perform. However, in order to collect money the attackers are leaving themselves open to investigation and tracing."
For protection, users should run security software and make sure that their software is patched, Websense and Symantec said. The Internet Explorer flaw exploited to attack the user in the Websense casein July last year.
The Websense customer was victimized two weeks ago. The Web sites involved in the attack have since been taken down.