Experts say another attack could be imminent and have warned people to ensure their security is up to date.
Microsoft in March released a patch for users to remove the vulnerability, but long-standing delays in updating major systems-such as the National Health Service (NHS) in the United Kingdom -exacerbated by a lack of support from the software company, allowed the attack to spread quickly around the world.
"We have stopped this one, but there will be another one coming and it will not be stoppable by us", the 22-year-old said.
The "WannaCry" attack grabbed headlines around the world because of its scale, but it's just one of many types of ransomware that cybersecurity experts see every day.
Russian Federation and Britain were among the worst-hit countries by the attack. Europol, the European Union's police agency, said the onslaught was at "an unprecedented level and will require a complex worldwide investigation to identify the culprits".
The spread of the worm dubbed WannaCry - "ransomware" that locked up more than 200,000 computers in more than 150 countries - began after hours on Friday Australian time, scrambling data and demanding payments of $300 to $600 to restore access.
A spokesperson for the organisation told Business Insider: "NHS Digital issued a targeted update on a secure portal accessible to NHS staff on April 25, and then via a bulletin to more than 10,000 security and IT professionals on April 27 to alert them to this specific issue". Normally, such patches are reserved for organisations willing to pay for extended support.
Patients are being told not to ring their surgery to check as they will be extremely busy.
Microsoft released security updates last month to address the vulnerability, with another patch released on Friday.
Apart from the police department, few other institutions, where non-upgraded versions of the Windows operating system has been in use, have also got affected due to the ransomware, the officer said. But computers and networks that haven't updated their systems are at risk. Avoid putting people into this situation in the first place by not sending links unless you have agreed prior to sending the email. This screen was photographed at Britain's National Health Service.
"We think Asia-Pacific was impacted probably not as heavily as the European regions, but I don't think they dodged a bullet", said Tim Wellsmore, Asia-Pacific director for threat intelligence at FireEye, a California-based network security company.
The crippling effects of WannaCry highlight a problem that experts have long known about, and one that appears to have hit developing countries harder.
High-profile victims include hospitals in Britain, the Spanish telecoms giant Telefonica, French carmaker Renault, US package delivery company FedEx, Russia's interior ministry and the German rail operator Deutsche Bahn.
The cyber criminals, whose identities are still unknown, also rebounded from the kill switch activation by releasing a second variation of the malware.
Short of paying, options for those already infected are usually limited to recovering data files from a backup, if available, or living without them. The flaw was first identified by U.S. intelligence. "But there's clearly some culpability on the part of the U.S. intelligence services".
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