PORTLAND, Ore. (KOIN) — A joint investigation between the US Post Office and the Washington County Sheriff’s Office is underway over the possibility skimming devices were illegally placed on self-service stamp machines at two post offices.

Three customers who all used self-service postage machines in Beaverton and Aloha over the last five days reported large fraudulent withdrawals on their ATM cards.

Skimming devices are typically chips covertly installed over the machine’s card slot, so that a customer’s card information can be read and stored when using the machine.

“It seems very suspicious obviously and I think it’s probably more than a coincidence, although we don’t’ have any evidence to tie them together,” said Washington County Sheriff’s Office spokesperson Bob Ray.

Card skimmers at Washington County post offices?