This warning follows an increase in the number of customers who are being duped at ATMs.

Standard Bank was the first local bank to introduce ATM screens that warn customers if the machine has been vandalised. In addition, ATMs that have been tampered with will shut down.

Since the introduction of this innovation to its ATMs nearly two years ago Standard Bank has seen a dramatic reduction in the vandalism of its ATMs. Criminals usually tamper with ATMs to make it easier for them to obtain customers' ATM cards.

"The fact that our ATMs are virtually tamper-proof has resulted in criminals using other devious means to obtain bank cards from our customers. We are starting to see the return of card-swap scams," says Les Barrett, manager, Standard Bank ATM Claims Centre.

He says criminals are now pretending to be bank customers who have just used the ATM successfully, thus making genuine customers less suspicious of the thieves and therefore less on their guard.

"Customers are lulled into a false sense of security. They believe the person offering to help is a customer. This makes them a lot more trusting of the criminal," says Barrett.

The criminal typically will inform the customer that there is a problem with the ATM and offer to show the customer how to insert his or her card to get the machine to operate again. The criminal will then swap the customer's card with another stolen card without the customer even being aware of what has happened.

The criminal then inserts the stolen card in the ATM and tells the customer to enter his or her PIN (personal identification number). After several unsuccessful transaction attempts the machine will retain the card. The customer then leaves believing that their card has been swallowed.

Armed with the customer's card and PIN, the criminal then goes to another ATM and plunders the customer's account.

Another common variation of this scam is the criminal will insert a stolen card, which has not yet been reported stolen, in the ATM just prior to the customer using it. When the customer tries to insert his or her card, the criminal will offer to assist. He will then swap the customer's card with another stolen card and advise the customer to enter his/her PIN. The criminal then has the customer's card and PIN.

Criminals usually carry out these scams at weekends and long weekends to give them several days' access to customers' accounts as customers usually only report the matter to the bank on Monday morning. More than 60% of all ATM claims at Standard Bank are received in the period around the traditional salary dates (from the 20th to the 4th next month).

Barrett says that up to 90% of ATM crime cases being reported to the ATM Claims Centre involve card swaps.

"Customers should always check that the bank card in their possession is theirs and, most importantly, they should under no circumstances accept help when transacting at an ATM."