In the case of the WannaCrypt attack, a tool developed by the U.S. National Security Agency was used to spread the ransomware to unpatched computer systems around the world. "It's a massive reminder to sectors right across the world cyber security should be a topline strategic priority".
It was too early to say who was behind the onslaught, which struck 100,000 organizations, and what their motivation was, aside from the obvious demand for money.
People in Lancashire and South Cumbria were warned to expect some disruption to GP services on Monday as IT and clinical systems were brought back online following the cyber-attack. It demands users pay United States dollars 300 worth of cryptocurrency Bitcoin to retrieve their files, though it warns that the payment will be raised after a certain amount of time. But overseas, high-profile organisations were affected, among them Russia's interior ministry, the U.S. logistics firm FedEx, Nissan and Hitachi in Japan, Britain's National Health Service and the Spanish telecommunications operator Telefonica.
Chinese media reported Sunday that students at several universities were hit, blocking access to their thesis papers and dissertation presentations.
The list of institutions affected has grown as more become aware of hacks and variants of the virus spread.
Nonetheless, the experts say such widespread attacks are tough to pull off.
Researchers who helped prevent the spread of the malware and cybersecurity firms worked around the clock during the weekend to monitor the situation and install a software patch to block the worm from infecting computers in corporations across the U.S., Europe and Asia.
The researcher tweeted that he initially didn't know that his actions would stop the malware. Our key direction to you is to remember that we are in this with our customers - we are trusted advisors, counselors, and suppliers to them.More news: Jimmy Carter urges Trump to push for peace
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Experts were scrambling to determine who was behind the attack, which exploited a security flaw in older versions of Microsoft's Windows operating software. Those include a known and highly unsafe security hole in Microsoft Windows, tardy users who didn't apply Microsoft's March software fix, and malware created to spread quickly once inside university, business and government networks.
It is highly critical of the way governments store data on software vulnerabilities. However, many organizations - including hospitals - had not appropriately updated their systems.
"As staff go back to work tomorrow, the HSE is advising all of its staff to "turn on" their computers but "do not log in" for a full two hours". That move, which cost just $10.69, redirected the attacks to the server of Kryptos Logic, the security company where he works.
The organisation also said that many organisations had failed to keep their systems up to date, allowing the virus to spread. Intelligence officials wouldn't comment on the authenticity of the claims.
"It's very important everyone understands that all they (the hackers) need to do is change some code and start again".
Those running Windows - or, realistically, any other operating system - are advised to ensure they are running the latest security patches available, have anti-malware software installed and activated, and have up-to-date backups which are stored offline, the latter being by far the best defence against ransomware attacks such as WannaCry and its predecessors.
Smith said Microsoft has the "first responsibility" to address the problem. Brad Smith criticized USA intelligence agencies, including the CIA and National Security Agency, for "stockpiling" software code that can be used by hackers. Security agencies in affected countries were racing to find out.
Hitachi: The Japanese electronics firm said Monday that its computer systems have been experiencing problems since the weekend, including not being able to send and receive emails or open attached files. "It's a handy thing to have, but it's a unsafe thing to have". That way, if your machine gets infected and your photos and documents are encrypted, you don't need to worry about losing them.