Cyber attack causes chaos worldwide, Australians warned they are at risk

A massive cyber attack has crippled computer systems in nearly 100 (99) countries. Experts say unknown hackers targeted a vulnerability, allegedly first exploited by the U-S spy agency, the National Security Agency (N-S-A).

The National Health Service (NHS) in Britain has been hit by a major cyber attack on its computer systems Source: (PA Wire/AAP)