Computer experts are warning people to be vigilant about a type of cybercrime known as "ransomware."
Hackers take control of a computer, or a computer network, and demand a ransom to release control of the device.
They use malware to infect the computer and deny access to its owner. The malware is activated after a computer user clicks on a compromised website, or opens an email sent by the criminals.
The hackers target individuals and businesses. The targets are often smaller businesses or government agencies that do not have sophisticated computer protection.
Recently hackers took control of a Hollywood hospital's computers. They demanded payment of 40 bitcoins, worth around US$17,000.
The advice from law enforcement is not to pay the ransom. But US computer experts believe a growing number of victims are paying up.
There are ways to try to stay safe and beat the hackers.
Always be careful about what attachments you click on. Keep your anti-virus software up to date and back up your files.
Netsafe has advice on ways to protect your computer from cybercrime.