British hospitals suffer major cyber attack - What we know so far

Britain's National Health Service said it had suffered a major cyber attack on Friday, disrupting hospitals all over England.

The health service said it had been hit with malicious software known as 'ransomware' that locks up computers and demands ransoms to restore access, but that so far it did not believe patient data had been accessed.

Here is what is known about the incident so far:

* Hospitals have reported major disruption to their IT systems. People have been asked not to visit unless they need immediate medical attention.

* The attacks span the length of England. The NHS said 16 of its organisations - some containing several hospitals - have been affected.

* It was not immediately clear whether patients had suffered as a result of the attack.

* In addition to London, there have been media reports of problems in Northumbria in the north east, Merseyside in the north west, and Essex in the south. There are no reports of attacks in Scotland or Wales so far.

* The National Health Service said it was a "ransomware attack" - a type of extortion. Computer users are locked out of their software and asked to pay up large sums of money to regain control. It said it believed the malware variant is called "Wanna Decryptor".

"The Trust has been advised by I.T. security and NHS-Digital of a serious Ransomware threat currently in circulation throughout the NHS," the email to employees of Britain's National Health Service said.

* Spain's government warned that a large number of companies had been attacked by cyber criminals who infected computers with "ransomware".

* The NHS said it did not have any evidence that patient data had been accessed.

* A reporter from the Health Service Journal said the attack had affected x-ray imaging systems, pathology test results, phone and bleep systems, and patient administration systems.

* Britain's National Crime Agency said it was aware of the reports of a cyber attack but made no further comment.