And now, ransom for PC virus

Kidnappers used to make ransom notes with letters cut out of magazines. Now, notes simply pop up on your computer screen, except the hostage is your PC.

Kidnappers used to make ransom notes with letters cut out of magazines. Now, notes simply pop up on your computer screen, except the hostage is your PC.

In the past year, hundreds of thousands of people across the world have switched on their computers to find distressing messages alerting them that they no longer have access to their PCs or any of the files on them.

The messages claim to be from the Federal Bureau of Investigation, some 20 other law enforcement agencies or, most recently, Anonymous, a shadowy group of hackers. The computer users are told that the only way to get their machines back is to pay a steep fine.

And, curiously, it's working. The scheme is making more than $5 million a year, according to computer security experts who are tracking them. The scourge dates to 2009 in Eastern Europe. Three years later, with business booming, the perpetrators have moved west.

The threat, known as ransomware, recently hit the United States. Some gangs have abandoned previously lucrative schemes, like fake antivirus scams and banking trojans, to focus on ransomware full time.

Essentially online extortion, ransomware involves infecting a user's computer with a virus that locks it. The attackers demand money before the computer will be unlocked, but once the money is paid, they rarely unlock it.

The hunt is on to find these gangs. Researchers at Symantec said they had identified 16 ransomware gangs. They tracked one gang that tried to infect more than 500,000 PCs over an 18-day period. But even if researchers can track their Internet addresses, catching and convicting those responsible can be difficult. NYT