10:59

The “accidental hero” who halted the global spread of an unprecedented ransomware attack by registering a garbled domain name hidden in the malware has warned the attack could be rebooted.

The ransomware used in Friday’s attack wreaked havoc on organisations including FedEx and Telefonica, as well as the UK’s National Health Service(NHS), where operations were cancelled, X-rays, test results and patient records became unavailable and phones did not work.

But the spread of the attack was brought to a sudden halt when one UK cybersecurity researcher tweeting as @malwaretechblog, with the help of Darien Huss from security firm Proofpoint, found and inadvertently activated a “kill switch” in the malicious software.

The researcher, who identified himself only as MalwareTech, is a 22-year old from south-west England who lives with his parents and works for Kryptos logic, an LA-based threat intelligence company.