Are you one of the 40 million?

A data breach at Target stores left millions of people who shopped at brick-and-mortar stores from November 27 to December 15 vulnerable to bank card theft.

Nick Kieffer, senior vice president at Landmark Bank, said breaches vary from case-to-case, but offered a general explanation.

"Somebody was able to gain access to a system, a software or a piece of hardware that might've been storing card data on it," Kieffer said.

Frances Freeman is one of the 40 million affected shoppers.

"Because it's Christmas...and I've used the credit and the debit card, both," Freeman said.

"It's scary because you can't even use your credit or debit cards without worrying about somebody hacking into them. And then they compromise your credit...I mean your whole life basically."

For Jack Calvert, the situation is all too familiar. His card information was stolen during the Scnucks breach earlier this year.

"Cash always works best, but it's not always available to do that so I guess you just have to be as careful as you can be. Stay on top of the charges," Calvert said.

Kieffer had similar advice for those who shopped at Target during the specified time period.

"They just need to look at account activity. They can do that either via online, via their mobile phone, call us or drop into one of our branches. But just be checking their transactions to make sure those are the transactions they've completed," Kieffer said.

Kieffer said right now Landmark Bank is monitoring their customers' accounts for fraud the same as they normally would.

They are waiting for more information before deciding their next step.

"Basically we're waiting for information from our partners...Visa and Target are researching at this point in time and any information they can share with us we'll appreciate and then change course or direction depending on what they send us," Kieffer said.