Tech-support scammers, fraudsters who claim to offer a legitimate online support service, often target users via cold calls or through pop-up windows on a computer.
Action Fraud, the UK's national fraud and cyber crime reporting centre, has received reports of tech-support scammers claiming to be from Microsoft who have so far conned one victim out of hundreds of pounds.
Detective Inspector Benn Kemp, of West Yorkshire Police's Cyber Crime Team, said: "Cyber crime is a rapidly expanding area and takes many different forms. The reality is however, that the vast majority of cyber crime can be prevented if people are aware of certain threats and situations where you could become a victim.
"I would urge members of the public to be on their guard when surfing the web and if you come across this message on your screen, report it to Action Fraud immediately."More importantly, ignore the instructions within the message. Microsoft warning messages will never include a phone number and Microsoft will never reach out to you proactively to provide technical support."
The latest victim fell for the scam when a pop-up window on their PC screen said it had been affected by WannaCry Ransomware - the malware that spread to more than 100 countries last month including the UK's NHS trusts - and provided a helpline for the victim to call.
The pop-up window wouldn't close when the victim tried to shut it down so the victim rang the contact number.
During the call, the fraudsters convinced them they didn't have sufficient antivirus protection and persuaded the victim to grant them remote access to their PC.
The fraudsters then installed a Windows Malicious Software Removal Tool - a freely available tool - and took Â£320 as payment.
Action Fraud is advising online users not to call numbers from pop-up messages, and never allow remote access to computers.
People should also never divulge passwords or pin numbers - and users are being reminded that Microsoft or someone their behalf will never contact people directly.
If you have been a victim of fraud or cyber crime, visit www.actionfraud.police.uk