More than 500 allegations of bank card cloning linked to a Bournemouth petrol station go as far afield as Taiwan and Australia, police have said.
The Malthurst Westview service station was shut after at least 25 people called police on Bank Holiday Monday.
Two Bournemouth men were later arrested on suspicion of conspiracy to defraud.
Cash is also alleged to have been fraudulently withdrawn in Egypt, Malaysia, Canada, Portugal, China, the US and the Netherlands, police said.
As part of the probe people have been asked to check their bank or card statements.
A police spokesman said: "Dorset Police is investigating more than 500 cases of alleged bank card cloning."
Officers from the force's cheque and card unit are now liaising with the Association for Payment Clearing Services (Apacs) - the UK trade association for payments.