Computer files 'held hostage'

2005-05-24 10:53

Washington - Computer users already anxious about viruses and identity theft have new reason to worry: Hackers have found a way to lock up the electronic documents on your computer and then demand US$200 over the internet to get them back.

Security researchers at San Diego-based Websense Inc uncovered the unusual extortion plot when a corporate customer they would not identify fell victim to the infection, which encrypted files that included documents, photographs and spreadsheets.

A ransom note left behind included an e-mail address, and the attacker using the address later demanded US$200 for the digital keys to unlock the files.

"This is equivalent to someone coming into your home, putting your valuables in a safe and not telling you the combination," said Oliver Friedrichs, a security manager for Symantec Corp.

The FBI said the scheme, which appears isolated, was unlike other internet extortion crimes. Leading security and anti-virus firms this week were updating protective software for companies and consumers to guard against this type of attack, which experts dubbed "ransom-ware".

"This seems fully malicious," said Joe Stewart, a researcher at Chicago-based Lurqh Corp, who studied the attack software.

Stewart managed to unlock the infected computer files without paying the extortion, but he worries that improved versions might be more difficult to overcome. Internet attacks commonly become more effective as they evolve over time as hackers learn to avoid the mistakes of earlier infections.

Locked up 15 types of data files

"You would have to pay the guy, or law enforcement would have to get his key to unencrypt the files," Stewart said.

The latest danger adds to the risks facing beleaguered internet users, who must increasingly deal with categories of threats that include spyware, viruses, worms, phishing e-mail fraud and denial of service attacks.

In the recent case, computer users could be infected by viewing a vandalised website with vulnerable internet browser software.

The infection locked up at least 15 types of data files and left behind a note with instructions to send e-mail to a particular address to purchase unlocking keys.

In an e-mail reply, the hacker demanded US$200 be wired to an internet banking account. "I send program to your email," the hacker wrote.

There was no reply to e-mails sent to that address on Monday by The Associated Press.

FBI spokesperson Paul Bresson said more familiar internet extortion schemes involve hackers demanding tens of thousands of dollars and threatening to attack commercial websites, interfering with sales or stealing customer data.

- AP