Fraudsters pretending to be Covid-19 contact tracers are calling and demanding money for bogus tests.
This is one of multiple coronavirus scams being used to target the vulnerable in Wales.
Police say criminals are pretending to be from organisations including the World Health Organisation and Netflix.
Stephen Jameson, 54, was shielding because of a heart condition and diabetes. He has been targeted by three separate Covid-19 scams.
He received a call from a bogus contact tracer saying he had been in contact with someone with coronavirus.
"He said, we need your data, I said I'm not giving you any of my information," said Mr Jameson, from Newport.
"He said, we need all your friends' information so we can contact them, and I said I haven't been out so you've got your information wrong.
"He said, you'll have to go and get a test, I need payment of £99 for the test."
Stephen, a former computer programmer and call centre manager, spotted the call was a scam.
He said: "He actually came over quite genuine, and the way they portrayed themselves, it was all the right sort of words. He then became abusive, so I put the phone down."
Stephen has also been sent fake texts saying his accounts have been frozen, and emails pretending to collect money for a "Covid-19 relief fund."
Police warned criminals are pretending to be from HM Revenue and Customs, the World Health Organisation, even Netflix and Amazon.
Action Fraud, the national fraud and cyber crime reporting centre, has received 2,521 reports of coronavirus related fraud with victims losing a total of £8,160,598 to criminals.
Gwent Police Cyber Security Team said the most common types of fraud were selling online protective face masks and hand sanitiser that do not arrive, phishing emails and texts, and bogus free school meal messages.
Det Ch Supt Clinton Blackburn is head of economic crime at City of London Police.
That is the national lead force for fraud.
He said coronavirus provided new opportunities for criminals.
He said: "We've seen a real mix, we've seen some people who are completely new to committing criminality, but equally there'll be offenders that were already offending in the fraud sphere but they've just turned their hand to the current pandemic.
"We've also seen other areas of fraud that have come to a halt, because people have been in lockdown so they weren't able to commit some of the frauds."
He added: "Anyone who's had anything to do with Covid in one way or another they've absolutely exploited. We would really urge people to take five minutes to think before you part with your cash."
The Welsh Government advised contact tracers abided by strict rules.
It said they would not ask people to dial premium rate numbers; make payments; ask for bank details, passwords or pin numbers.
They also would not provide medical advice; ask people to download software; or access non-government or NHS websites.