Experts say card fraud is usually carried out by organised gangs

Thieves use an electronic device they attach to a machine to record card details, which they use to produce a fake card to go on a spending spree.

They can then make fraudulent purchases in shops or on the internet.

The warning by Dorset Police comes after a number of high street banks in Old Christchurch Road, Bournemouth, Dorset, were targeted.

Thieves also monitor some machines with a camera to record PIN details.

Inspector Neil MacBean, of Dorset Police, said: "One technique being used by criminals involves displaying 'Out of Order' signs on surrounding cash machines, forcing people to use the one that they have fitted with their card-cloning device.

"Tell-tale signs that a cash machine might have been tampered with include a larger than normal card slot, wires protruding from the machine or an attached box that could contain a small digital camera to take photos of your PIN being entered."