CHICAGO (CBS) — Authorities in Aurora are investigating two cases of skimmers attached to ATM machines at local banks.

Skimmers are used to steal credit card, debit and PIN numbers by grabbing data from the magnetic stripes of the cards.

The first one was found Saturday morning around 6:30 at the Farnsworth branch of Old Second Bank.

A bank employee saw a woman walking up to an ATM who began to act suspiciously. Shortly thereafter the woman left the area. The employee found the skimmer and notified the bank which alerted other branches.

A short time later a skimmer was found at the bank’s Fox Valley branch.

It’s not known if accounts were compromised. Aurora police are looking through surveillance video at the bank and will release more information as it becomes available.

Aurora police said if you notice that information was stolen from an account, report it to the bank and/or credit card company.