CHICAGO (CBS) – In the past week skimmers, which can steal debit card information, have been discovered on ATMs at three Walgreens stores.

Inside the Walgreens at Monroe and Clark, an “out of order” sign comes one day after a customer, according to police, found a skimmer attached to the machine.

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A skimmer covers the slot where a card is inserted. It allows thieves to read and steal information.

“I’m surprised to hear that,” said Andrea Bacon. “Since it’s inside a Walgreens.”

Someone has hit three Walgreens stores in the Loop. Last Thursday, at the store on Madison and Wells an ATM maintenance worker, responding to an alert of tampering, found both machines with skimmers attached.

That same day, at the company’s flagship store on State Street, another skimmer was found.

“Somebody sees this as a valuable target.”

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Jeremy Hajek is a professor of information technology at the Illinois Institute of Technology.

“If there are multimillionaires, CEO’s using that, you’d want to take their account if you’re a criminal,” said Hajek.

He added that everyone needs to take precautions. Before using any ATM, examine the keypad.

“Equipment has wear patterns. A lot of people touch it,” said Hajek. “But it looks brand new, that may be clue that something may be a bit odd.”

And don’t be afraid to shake the slot.

“Try and tug a little bit and see if something comes off,” said Hajek.  “Make sure everything is as it appears to be.”

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Police have tips for spotting skimmers. If there’s trouble inserting a card, do not use that ATM. People should cover the keypad when entering a PIN number because sometimes thieves can hide a camera above the keypad.

Dorothy Tucker