Credit card fraudsters are trying to fleece UK punters by tricking them into revealing card security information over the phone. The fraudsters, posing as representatives of Visa, are already is possession of card numbers and are after the CVV numbers (commonly printed on the signature panel on the back of the card) often needed to make purchases online.
The full article is here: http://www.theregister.co.uk/2004/11/22/visa_scam/

You would have to beat my pin number out of me with a rubber trunchion but i have had to give the cvv number out over the phone befor, during a purchase . This scam could well fool a few people.