The Federal Trade Commission, FBI and other federal agencies are warning consumers and businesses about a malware program known as "Cryptolocker" that locks up computer files and holds them for ransom.
Cryptolocker encrypts everything on a hard drive and in shared folders. When the job is done, the user gets a note demanding payment via Bitcoin or other anonymous payment methods to unlock them.
The typical "ransom" is $300, the FTC said.
"Criminals behind this malware say they'll give you the encryption key if you pay, but they're hardly trustworthy," the agency said. "And there's no other way to unlock your files."
The malware is spread mostly through links in emails and undetected downloads when visiting infected websites. Emails might look like routine messages from a legitimate company, such as a tracking notice from a shipping company.
The best way to minimize damage from Cryptolocker is to back up computer files often, the agency said.
For tips on how to avoid, detect, and get rid of malware, go to www.consumer.ftc.gov/blog/back-back-back-it. For tips on protecting a business from Cryptolocker, try "Lock, stock and peril" at www.ftc.gov.