A massive cyber-attack hit National Health Services in the United Kingdom on Friday. The cyber-attacks appear to have have affected several organisations worldwide. British Prime Minister Theresa May said that the hacks were not specifically targeted at NHS, and that many organisations and countries have been affected by it.

The attacks affected as many as 74 countries and at least 16 NHS trusts in UK. It seems to have been carried out by hackers by using a tool stolen from the National Security Agency in United States, reported The Guardian.

The cyber attack led to chaos in some places, with appointments being cancelled, patients being turned away and phone lines being disrupted. NHS Digital said the hackers used a malware called the Wanna Decryptor, AP reported. However, NHS Digital, which runs the services’ cyber security, said they were not specifically the target of the attack. In a statement, the NHS said they are investigating the attack but added that they have not found any evidence to prove “patient data has been accessed.”

The IT systems of these hospitals went down simultaneously. Pop-up messages saying, “Ooops, your files have been encrypted,” followed, with demands for money from the organisations, The Guardian reported. It added that the hackers were asking for $300 in bitcoin.

NHS had reportedly ignored multiple warnings that many of its computers were outdated and unprotected. The operating system in most of these computers is Windows XP. Besides, a government contract with Microsoft to update the software for NHS had expired in 2014, reported The New York Times.

Besides the NHS, some Spanish companies have also been affected by the hacks. Telecom company Telefonica was one such firm. Later, reports also poured in from Portugal, Russia, Ukraine and Taiwan. Kaspersky Lab, a cyber security firm in Moscow, said that around 45,000 attacks had been carried out in 74 countries.