An investigation is underway after a Harrisonburg grocery store discovered it was fooled by counterfeit $20 bills.

"At first glance you may not recognize it, but when you start looking at it you could definitely tell it's not real, and when we use the counterfeit pen on it, it turned black right away," says Red Front Store supervisor Cindy Bolton.

The store says a woman, captured on surveillance camera, used counterfeit $20 bills to pay for her merchandise, and then left the store. Though store employees were shocked, this isn't the first time they've come across fake bills.

"We had one a long time ago, but this is the worst we have had, and apparently it's something common in this area. Unfortunately," says Bolton.

The secret service is working the case, and member say others cases like it are becoming more common.

"We've experienced a slight increase over the past couple of months," says Joseph Morrison, the assistant to the special agent in charge for the Richmond Secret Service Field Office.

During this type of tough economy, the question looms about whether or not more counterfeit crimes may occur.

"I'd rather not speculate on why the counterfeit is being passed,' says Morrison.

Whether a tight economy is the culprit or not, Morrison says technology will continue to make counterfeiting, easier.

"Over the past few years, it's been relatively easy with the ink-jet printers they have out now. Most of our counterfeit bill come from the ink-jet printers," say Morrison.

In the future, Red Front Market will mark all bills that are greater than $1 to try and prevent more incidents like this.