Giving your credit card number to a website is not the dangerous act many people believe it to be. The biggest hazard is the receipts you get from using your credit or debit card in stores.

Because of the way online ordering works, all fraudsters need to become you, for as long as it takes to swipe your details, is a card number and an expiry date. These particulars are routinely printed on till receipts, and it is these receipts which are generating unauthorised debits for cardholders and headaches for the police.

"Credit card receipts in the wrong hands are as dangerous as £10 notes," said a police officer who works on internet card fraud. "People have got to realise credit card receipts pose a risk," he added. These receipts could then be used to buy goods online, or even over the phone.

All the major grocers have wised-up to this problem now. Tesco and Safeway both hash out the last four digits of a customer's credit card number for precisely this reason. Sainsbury's is behind the field, as it only moved from obscuring one digit to hashing out four this year, and not every Sainsbury's store is doing this yet.

But it seems grocers are not the big problem here. Smaller stores don't have this thinking, and the receipts from them are a prime source of online credit card fraud.