As if Monday's weren't back enough, computer users worldwide are finding their computers being held for ransom - 300-600 bitcoin to be exact.

Ransomware 'WannaCry' or 'Wanna Decryptor' is attacking old versions of Windows, and was first seen in Britain's medical networks Friday, according to the Washington Times.

Since then, over 150 countries have been affected, holding hostage computers which run integral parts of life such as factories, banks, government agencies and transport systems. Here in the U.S. FedEx Corp. was hit with the cyber-attack, while in Russia the Interior Ministry was held ransom and in Spain, company Telefonica got hit.

Worse than that are the hospitals in Indonesia and Japan. Dharmais Hospital and Harapan Kita Hospital in Jakarta, 16 plus hospitals in the U.K. were forced to stop work. En Chu Kong Hospital in Sanxia, New Taipei, Lakeridge Health in Oshawa, Ontario,

In China, the education sector was hit the hardest, 15 percent of their reported attacks were at universities and educational institutions, according to KTBS.

How did this happen? Hackers found a way through a security flaw in Microsoft's SMB networking protocol, according to the U.K.'s V3. Indonesia's Minister of Communication and Informatics, Rudiantara says that Ransomware is exclusive to old versions of Windows.

“The affected computers are those with old Windows, issued in 2008 or earlier. Computers with current operating systems, such as Mac, won’t be affected."

According to President Trump's Homeland Security Advisor, Tom Bossert, the attacks in the U.S. are under control. However, Bossert told Good Morning America that the concern is that more attacks like this will happen.

Microsoft is telling a different story, accusing U.S. intelligence of  "stockpiling" coding which offers an invitation to hackers to get into systems. Some cybersecurity experts are wondering if the vulnerability exposed with the leaked U.S. government documents could be part of the attraction.

Ironically, it is Kaspersky Labs that Interpol and Europol brought in for support, days after continuing speculation in the U.S. grew as to whether Kaspersky has Russian intelligence ties.

To ensure the safety of computers, IT experts recommend making sure your Windows platform is current and that all files are backed up regularly.