An investigation is taking place after a bundle of store receipts containing confidential customer details was found on the street in Bournemouth town centre.
All are retailers' copies of debit card transactions ranging from £13.50 to £50 carried out at clothing shop Oasis in Old Christchurch Road on a single day.
Each includes the full card number, expiry date and customer's signature.
The person who picked them up in Post Office Road on Wednesday night handed them over to the Daily Echo with the comment: "What a wonderful haul, had these ended up in the hands of a crook.
"All of the cards on the slips are still valid. I collected up all I could.
"However, many more could have been picked up by other people."
Anna Harding, assistant manager of the Bournemouth store, said: "We will find out exactly how these have come to be out of our store.
"Obviously it's quite a concern for us."
The Daily Echo also alerted Oasis' head office to the breach of security and has now passed on the receipts to Dorset Police.
Sergeant Richard Niemier, of the cheque and credit card unit, said: "It concerns me. We need to be doing a bit of research to find out if these accounts are safe.
"It could be that they have been compromised and fraud is being committed.
"We would like to follow it up because it sounds to me that this kind of information could be available to fraudsters."