The Office of Fair Trading (OFT) warned that just over four million adults in the UK have responded to a scam, of which a third lost money as a result.
OFT chief executive John Fingleton said: "Scammers are using ever more sophisticated tactics to dupe people out of their cash. We want people to recognise the warning signs, and seek advice from friends or from Consumer Direct."
Research by the OFT found that around half of those who fell prey to scams lost more than 50, while 5 per cent lost more than 5,000. Specialist trading standards teams have been created to crack down on the worst con tricks.