Spain also reports ransomware attack

He added that the company managed to restore the work of its call center but closed most of its offices for the day. There are no reports of attacks in Scotland or Wales so far. The committee, the nation's top investigative agency, has rejected the claim.

Following the cyber attack, hospitals cancelled appointments and turned away patients, asking them to come only if it was an emergency. Hospitals, with their often outdated IT systems and trove of confidential patient data, are a particularly tempting target.

It also hit major corporations, including Spanish telecoms giant Telefónica - the parent company of the United Kingdom mobile network O2 - as well as computer systems in Russian Federation, the USA, Japan, and France.

In Spain, some big firms took pre-emptive steps to thwart ransomware attacks following a warning from Spain's National Cryptology Centre of "a massive ransomware attack".

"Infection of a single computer can end up compromising the entire corporate network", Spain's Computer Emergency Response Team says.

Mrs May said: "We are aware that a number of NHS organisations have reported that they have suffered from a ransomware attack".

NHS employees and health journalists are tweeting images of the apparent ransomware, which is demanding $300 worth of Bitcoin to restore ransomed files.

"The key question" to consider is how an attack such as Friday's could originate "from a non-critical system such as email" and then spread to other systems, said Awais Rashid, a professor of software engineering at Lancaster University.

A patch for the vulnerability was released by Microsoft in March, but many systems may not have had the update installed.

The UK's National Health Service (NHS) was also hit by a ransomware attack and screenshots of the WannaCry program were shared by NHS staff.

"News (of this attack) has been exaggerated and our colleagues are working on it right now", Telefonica Chief Data Officer Chema Alonso, a well-known cyber security expert, said on Twitter. Having to cancel appointments and close entire hospitals is devastating for the industry.

A spokesman for Barts Health NHS Trust in London said it was experiencing "major IT disruption" and delays at all four of its hospitals.

"To ensure that all back-up processes and procedures were put in place quickly, the trust declared a major internal incident to make sure that patients already in the trust's hospitals continued to receive the care they need", a spokesperson for the trust said.

  • Leroy Wright