Fraudsters are targeting Sheffield shoppers by sending them fake gift vouchers claiming to be from the Sainsbury's supermarket.
Action Fraud, the UK’s cyber crime reporting centre, said numerous people across the UK have received emails purporting to be from the supermarket.
The message claims they have been overcharged during a recent visit to a store and have been sent a gift voucher as compensation
But when customers click the link to receive their prize they are led to a website that could potentially defraud them.
A spokesperson for Action Fraud said: "Reports have said the emails look genuine by using the victim’s first name.
"If you receive an email offering Sainsbury’s gift vouchers be wary and don’t assume anyone who has sent you an email is from the company who they say they are from.
"Check the sender’s email address as they may use an address that looks like it could be from the brand they’re impersonating
"Finally, report fraud and cyber crime and receive a police crime reference number."