A cyber virus which caused turmoil within the NHS could have been much worse, a computer expert at the University of Sheffield has claimed.
The Wanna Decryptor - or WannaCry - virus sent the health service into meltdown on Friday, with hospitals in parts of the country forced to cancel treatments and appointments.
The NHS was still recovering today, and although hospitals in Sheffield and Doncaster said they were unaffected, health chiefs in those areas asked members of the public to 'remain patient' as GP practices got back up to speed.
John Clark, professor of computer and information security at the University of Sheffield, said the attack should act as a wake-up call for the health service and for businesses and individuals to defend themselves adequately against so-called 'ransomware'.
He also said the NHS may have 'got away with it' to some extent, as its 'obsolete' computer systems could easily have been subjected to a targeted attack seeking to extract patients' personal data.
"I think we may have got away with it. The NHS has been lucky this time but it needs to take stock of where it's at," he said.
"This is a sophisticated attack in terms of how it goes about attacking systems but relatively simple in terms of what it does, which is to scramble data and charge a ransom for victims to unscramble that data.
"This was general purpose malware and not a targeted virus. Something more focused with knowledge of NHS systems could have done something much worse.
"This is a wake-up call for the NHS but also more generally to businesses around the country."
Professor Clark said ransomware represented a growing threat to computer users but pointed out that this virus was not new and a 'patch' had already been completed to protect newer operating systems but not 'obsolete' ones like Windows XP.
He said the NHS was particularly vulnerable as it is such a large organisation and the virus only needed 'one point of entry'.
But he claimed smaller businesses, many of which he said were 'technophobic', and individuals could do more to protect themselves too.
His advice is:
* If you are using an 'obsolete' operating system like Windows XP, pay to convert to Windows 10. It costs around £120 which sounds expensive but it's a lot better than having your data wrecked
* Don't click on links when you're not sure where they lead
* Never pay a ransom. Aside from encouraging cyber criminals, you have no idea what they will do once you have paid
* Back up your system regularly, preferably onto external hard drives
Professor Clark said more information on protecting your computer was available via the IT security company Sophos and the National Cyber Security Centre, among other sources.