South Australian police are hunting a man who used stolen credit cards by simply 'guessing' the pin numbers from information kept in the their owners' bags or wallets.

The cards were taken in a series of thefts from around the McLaren Vale area, on South Australia's Fleurieu Peninsula.

The man has been spied calmly using the cards at the ANZ ATM on Main Rd at McLaren Vale, on CCTV footage.

He already knows the correct pin numbers, and withdraws the cash easily.

Credit Union SA Chief Executive, David White, said while it is hard to remember PIN numbers in today's world of passwords, the most common mistake people make is using their date of birth or phone number.

"The best thing you can do is pick a number that's easy for you to remember and remember it, don't write it down," he said.

"Family members, as much as you love and trust them, even there you shouldn't disclose your PIN to anybody other than yourself"

The cards were from seven wallets stolen from the McLaren Vale Primary School on Main Rd at McLaren Vale on Wednesday July 6, between 11.30 and 12.00pm, and from the McLaren Vale Hospital between 2.15pm and 2.30pm on Tuesday July 19.

The man is described as being Caucasian, 183cm tall, average build with dark collar-length hair and thick eyebrows.

Police are asking anyone with further information on the thefts to contact BankSA Crime Stoppers on 1800 333 000 or go to their website.