The virus exploits a flaw in a version of Microsoft Windows first identified by U.S. intelligence.
"An equivalent scenario with conventional weapons would be the USA military having some of its Tomahawk missiles stolen", wrote Brad Smith, President and Chief Legal Officer. Microsoft requires Windows 10 customers to automatically update their computers, but some people with older PCs disabled automatic updates.
"As cybercriminals become more sophisticated, there is simply no way for customers to protect themselves against threats unless they update their systems", Smith wrote.
The British government said 48 of the 248 health service trusts in the United Kingdom were impacted by Friday's attack.
On Monday, a Microsoft spokesman declined to comment beyond Smith's post.
As for Microsoft, some intelligence agency experts questioned its NSA criticism, saying it's unreasonable for the company to ask governments to stop using its products as a way to attack and monitor enemies.
Also, make sure that you run an active anti-virus security suite of tools on your system, and browse the Internet safely.
There will be lessons to learn from what appears to be the biggest criminal cyber-attack in history, Rudd said cited by Bloomberg in response to a letter from Jonathan Ashworth, the shadow secretary of state for health.
"People have extremely short memories when it comes to this", said Jan Dawson, an analyst with Jackdaw Research.
"At the moment we are in the face of an escalating threat, the numbers are going up, I am anxious about how the numbers will continue to grow when people go to work and turn their machines on Monday morning".
The company's top lawyer said the government should report weaknesses they discover to software companies rather than seek to exploit them.
According to Bloomberg, a year ago an acute-care hospital in Hollywood paid $17,000 in bitcoin to an extortionist who hijacked its computer systems and forced doctors and staff to revert to pen and paper for record-keeping.
Those clues could point to it being the work of an established group, he said, but there was little sign of any tell-tale text in the version now circulating.
Microsoft released a patch for the flaw in March after hackers stole the exploit from the NSA.
Scott Vernick, a data security lawyer at Fox Rothschild, said businesses that failed to update their software could face scrutiny from the US Federal Trade Commission. "The money they made from these customers hasn't expired; neither has their responsibility to fix defects".
Keep security software up to date. Numerous affected parties were found operating unsupported Windows versions without bothering to update to supported ones.
Dr Anne Rainsberry, NHS incident director, said: "We have been working with 47 organisations providing urgent and emergency care who have been infected to varying degrees".
Most victims were quickly able to recover infected systems with backups, said the group's chief economist, Scott Borg.
"Expect to hear a lot more about this tomorrow morning when users are back in their offices and might fall for phishing emails" or other as yet unconfirmed ways the worm may propagate, said Christian Karam, a Singapore-based security researcher.
A Nissan auto factory in the north-eastern city of Sunderland was also affected, a spokeswoman said.