The ransomware, which goes by the name WannaCrypt and similar names, infected 1,000 computers in Russia's Ministry of Internal Affairs, along with machines at Great Britain's National Health Service, and the Spanish telecom provider Telefonica, Forbes reported.
The attack is likely to prompt more organizations to apply the security fixes that would prevent the malware from spreading automatically.
McGary said the hospital network has a contingency plan for tech problems and it was "business as usual".
FILE - A security specialist works at a computer station with a cyberthreat map displayed on a wall in front of him in the Cyber Security Operations Center at AEP headquarters in Columbus, Ohio, May 20, 2015.
Keep security software up to date. "We think it's going to be the footprint for other kinds of attacks in the future". But some experts have argued this attack could have been vastly mitigated if the NSA told Microsoft sooner. While there's been limited public declaration (expect many are keeping quiet) that Australian users have been impacted on a large scale, it does speak to the lack of updating that's happening to connected systems. "An equivalent scenario with conventional weapons would be the USA military having some of its Tomahawk missiles stolen".
Patch your computers. They should have the latest software update.More news: Chest injury won't force Cleveland Indians' Carrasco to miss a start
Companies and institutions are often slow to update their computers because it can screw up internal software that is built to work with a certain version of Windows.
Rounding out the five, Barracuda Networks Inc., which sells security software specifically focused on email, the main path through which WannyCry spread, closed the day up 5.7 percent. The WannaCry infection does not affect those using Macintosh computers.
The attack held users hostage by freezing their computers, encrypting their data and demanding money through online bitcoin payment - $300 at first, rising to $600 before it destroys files hours later.
FILE - A Microsoft logo is seen on an office building in New York City, July 28, 2015.
The ransomware appeared to exploit a vulnerability in Microsoft Windows that was purportedly identified by the U.S. National Security Agency for its own intelligence-gathering purposes.
The attack largely infected networks that used out-of-date software, such as Windows XP, which Microsoft no longer offers technical support for.
Microsoft declined a request for an interview, but a statement on the company's blog said: "Seeing businesses and individuals affected by cyberattacks, such as the ones reported today, was painful".
"The fact that so many computers remained vulnerable two months after the release of a patch illustrates this aspect", Smith wrote Sunday.
A deeper look into the Trojan's eruption reveals a callous disregard on Microsoft's part for users of its older operating systems.