Before 2014, ransomware viruses would typically just be an inconvenience for you and your IT company to clean up. Then CryptoLock appeared. The virus would encrypt your company files with an unknown password. Once infected you either have to recover from backups, pay the ransom or just lose the data.
NHS services across England and Scotland have been hit by a large-scale cyber-attack that has disrupted hospital and GP appointments.
The prime minister said the incident was part of an untargeted wider attack affecting organisations globally.
Some hospitals and GPs have been unable to access patient data, after their computers were locked by a ransomware program demanding a payment worth £230.