Hospital leaders across the country are warily keeping an eye on major hacks that are roiling the United Kingdom's hospital system.

The wariness comes as Britain's hospital systems are dealing with a ransomware hack in which users cannot access files unless they pay $300 in the online currency bitcoin. Many hospitals have had to cancel appointments and procedures, as the ransomware, known as "WannaCry," crippled their computer systems.

Hospital leaders are monitoring what is happening with the U.K., "using the lessons learned in previous attacks and applying best cybersecurity practices in an effort to anticipate and respond to existing and emerging threats," said Chantal Worzala, vice president of policy operations for the American Hospital Association.

A year ago, hospital networks in the Washington area, Kentucky and California were hit by a similar cyberattack, which was investigated by the FBI.

So far 74 countries have been hit by the ransomware attack, which may have been malware created by the National Security Agency and stolen by hackers earlier this year.

Experts have believed the Microsoft Windows exploit, known as "EternalBlue," was revealed as part of a leak by a hacking group, the Shadow Brokers, last month. Microsoft released a patch for the exploit in March, but only for computers running an operating system newer than Windows 7. The company encouraged users with older versions "to ensure their computers are up-to-date."

Many hospitals in the United Kingdom's National Health Service still use Windows XP, released in 2001, and there is concern that hospitals and other entities using older Windows operating systems in the United States are also vulnerable.