Trading standards officers in Cornwall have issued a warning that local residents are being targeted in a telephone scam.
Rogue traders have been contacting people and scaring them into believing their computers are infected by a virus.
The callers, posing as help desk staff from an IT company, appear to be randomly telephoning people and saying their computer needs immediate attention. Nigel Strick from Cornwall's Trading Standards Service, said a number of people have already been persuaded to part with fairly large sums of money.
"Victims are being left out of pocket and their computers seriously compromised," he said.
Mr Strick said the tactics to be on the look-out for was for the caller to tell a computer owner that they have been informed of a serious problem by an internet service provider and offer to fix it for a sum of up to £250.
They gain remote access to the computer and generate a false log indicating a major error has been repaired. However Mr Strick warned that by this time all the personal files on the computer had been accessed by the phantom IT help desk and this could mean bank or credit card details were compromised.