Scammers are taking control of people's computers and demanding payments to release them again.
Trading Standards officers said tens of thousands of users are falling victim to such scams - which begin when they ask for help with a printer error.
The fraudsters then claim to offer 'printer helplines', which consumers are fooled into contacting, which then allows scammers remote access to their computers.
In some cases victims have had personal information such as their bank details stolen or received demands for money if they want control of their computers handed back.
The scammers appear credible by claiming to have links with well-known computer and printer brands, and in one case they tried to charge a victim £700.
Mike Andrews, lead co-ordinator of the National Trading Standards eCrime team, is now urging South Yorkshire residents to be wary of the scam.
He said: "While victims expect they will receive help with their printer problems, they have in fact been lured into a trap, and find themselves at risking of losing money or important personal information and also have their computer security compromised."
Consumers are advised to visit the manufacturer's website to get official contact details for help with printer problems, be suspicious of helplines asking to take control of your computer and keep anti-virus software up to date.
In 2016 there were more than 32,000 such cases of computer service fraud.