ASPEN, Colo. (CBS4)- Police in Aspen are searching for skimming suspects after a skimmer was located at an ATM in an Aspen bank. An unknown number of credit cards may have been compromised and the suspects remain on the loose.

A skimmer is a small electronic device that copies the data from ATM cards inserted in ATMs or other automatic pay stations, such as gas pump station credit card readers.

The data copies then allows the creation of a duplicate and fraudulent credit card or ATM card.

The ATM in the lobby of an Aspen bank was compromised between Dec. 22, 2012 and Dec. 29, 2012.

“Because we are aware that criminal activity was occurring in town, it is possible that other credit card readers may have been similarly compromised,” said Aspen Police Detective Walter Chi. “We recommend that everyone check their bank accounts for fraudulent activity and to continue to monitor them.”

Chi advised customers of ATMs should also cover the keypad when entering personal identification numbers at ATMs.

The bank involved is cooperating with police and said they contacted all bank customers who used the ATM during that time and have issued them new cards.

Those who suspect fraudulent activity on their account are asked to contact the Aspen Police Department at 970-920-5400.

Investigators have released surveillance video of the skimming suspects.