(CBS) – She’d already had her credit card number stolen once, and it almost happened a second time.

But the actions one Chicago woman took when she saw something suspicious not only kept her from being victimized again, but likely helped others, too.

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CBS 2’s Dana Kozlov reports.

“I had walked up to the ATM and just jiggled the piece,” Jill Koenig explains.

It’s a typical security check for her, months after her credit card number was stolen. Usually, nothing happens when she checks the ATM. But this time, “it came right off, and I looked at the inside of it and could see the mechanism.”

The mechanism was a “skimmer,” a device that reads and steals credit and debit card information. Koenig found it last week, on a stand-alone ATM inside a Greek Town Walgreens.

She took pictures and told management.

“I was really in shock because I knew what I’d discovered,” she says.

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She also contacted the ATM’s bank on Facebook and posted her discovery.

“It just spread kind of like wildfire. People didn’t realize that these things are out there,” Koenig says.

Fraud expert William Kresse says skimmer scams have shot up more than 500 percent since 2014. One theory is thieves are scrambling to benefit before all card strips are replaced by chips.

“Once all ATMs use only the embedded chip, the ability to steal the account information off the mag stripe is useless,” he says.

Until then?

“Be more on the paranoid side and don’t worry about poking at the machine.”

Experts say if any part comes loose, don’t use the machine and report it.

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Kresse also says it’s best to avoid stand-alone ATMs. A Walgreens spokesperson tells us they take customers’ privacy seriously and are cooperating with law enforcement.