"Practically speaking, it's not possible to completely isolate the NHS network", said cyber-security expert Prof Alan Woodward. The BBC quoted one NHS staffer who said it was "absolute carnage" and that "patients will nearly certainly suffer and die because of this".
Some hospitals also use equipment with outdated software. For instance, if the link purports to be on a Microsoft security advisory but the link that pops up doesn't lead back to Microsoft's official websites but instead to some other dodgy website, you'll know that it's a malicious link.
"The attack is not focused on any particular industry but is widely spread, especially across those organisations, which are online and connected, ' Quick Heal Technologies" managing director Sanjay Katkar said. There's also no guarantee all files will be restored.
Problems with cyber security in NHS organisations were highlighted a year ago by Dame Fiona Caldicott, the national data guardian, who warned that issues were given insufficient priority and that health bodies persisted in using obsolete computer systems, The Times said.
How can I personally protect my device from ransomware?
"Even though it's becoming harder and harder, the incentives have increased tremendously", said Mador, who previously worked on security response at Microsoft.
However, there are measures that can be taken to protect those systems, like isolating them on network segments where access is strictly controlled or by disabling unneeded protocols and services.
Dore said companies that faced disruptions because they did not run the Microsoft update or because they were using older versions of Windows could face lawsuits if they publicly touted their cyber security.
Criminals will often use a widely publicised virus outbreak to send scam emails, pretending to offer help.
If you're not on a work network that already has security, consider installing some form of security program on your computer. But computers and networks that didn't update their systems are still at risk.
When Microsoft sells software it does so through a licensing agreement that states the company is not liable for any security breaches, said Michael Scott, a professor at Southwestern Law School. Then, just as quickly as it started, the attack was stalled by a 22-year-old British cybersecurity researcher who discovered a "kill switch" that stopped the ransomware from spreading.
The WannaCry attackers didn't put in a lot of work to build the SMB-based infection component either, as they simply adapted an existing exploit leaked in April by a group called the Shadow Brokers. While this is usually seen as a standard police issue, or for the Federal Bureau of Investigation to deal with, Rogers said ransomware was something that could become a military concern. Experts said this vulnerability has been known for months, and Microsoft had fixed the problem in updates of recent versions of Windows.
There's no denying, of course, that Washington does share some of the blame for the spread of the attack.
"Our key direction to you is to remember that we are in this with our customers - we are trusted advisers, counselors, and suppliers to them", he wrote.
Hackers find vulnerabilities in operating systems and try to exploit those vulnerabilities by tricking users into downloading malware or malicious code.
"Practice ABC - assume nothing, believe no-one, check everything", says Prof Woodward. He noted there was no indication the cyber attack had resulted in widespread disclosure of personal data.style="text-align: center;"