How the virus works

Ransomware is a type of cyber attack that locks all digital files and demands payment in order for them to be returned. Computers infected with a ransomware virus become unusable save for displaying a ransom note.

A variant of the Petya ransomware was blamed for yesterday’s global attack. Petya locks a computer’s hard drive and files stored on it. It is harder to recover information from computers affected by this ransomware.

Experts said the program could have spread like the Wannacry attack that hit hundreds of thousands of computers, including those used by the NHS.