Scammers are taking control of people's computers and demanding payments to release them again, consumers are being warned.
Trading Standards officers say that tens of thousands of users are falling victim to such scams, which begin when they ask for help with a printer error.
The fraudsters claim to offer "printer helplines", which consumers are fooled into contacting.
Typically, users then allow scammers remote access to their computers.
In some cases the fraudsters steal information - such as bank account details - or demand money to hand back control.
They appear credible by claiming to have links with well-known computer and printer brands.
In one case, they tried to charge a victim £700.
Another user was told that their online identity had been corrupted and all their passwords had been stolen. The "fee" to correct it was £200.
"This printer helpline scam scam is particularly pernicious because it encourages victims to unknowingly contact the fraudsters of their own accord," said Mike Andrews, lead co-ordinator of the National Trading Standards eCrime team.
"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."
In 2016 there were more than 32,000 such cases of computer service fraud, according to Action Fraud, which is a 47% rise since 2014.
How to protect yourself from printer scamsImage copyright Thinkstock
- If seeking technical support for your printer, visit the manufacturer's website to get the official contact details
- Be suspicious of helplines asking to take control of your computer to fix a printer problem
- Keep anti-virus software up to date, to stop pop-ups from bogus services
"I would urge people to be particularly vigilant about this scam," said Lord Harris, chair of National Trading Standards.
"If you are seeking help for printer issues you should always use the official printer helpline details provided when you bought the product or consult the official website of the manufacturer for helpline details."