'Accidental hero' halts ransomware attack and warns: this is not over

Expert who stopped spread of attack by activating software's 'kill switch' says criminals will 'change the code and start again'

• Massive ransomware cyber-attack hits countries around the world
• Criminals behind cyber-attack have raised just $20,000, experts say

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.