Several months ago a women's magazine arrived in our mailbox – with my husband's name on it. Curious, I asked him why he subscribed. “I didn’t,” he replied.

We never did figure out exactly why he received it, but the likely culprit was a Web site from which he had purchased business cards. The site employs a tactic where a series of check boxes follow your order. If you fail to notice and do not uncheck them, you have “signed up” for the magazine.

In our case, I planned to do battle once the bill arrived, but it never did. I assume the magazine was just trying to add numbers to its subscription figures to help entice advertisers.

But imagine if the business card printer had given my husband’s credit card number to the magazine publisher and a charge for the subscription appeared on this credit card bill. We both would've flipped.

Unfortunately, that's not as far-fetched as it sounds. This practice is called “data pass,” and it was the subject of a Senate Commerce Committee hearing in November 2009. Here’s how it works: You make a purchase online and immediately after, you get an offer for a “rebate,” “reward,” “discount club” or something similar. If you accept, you are signed up and your credit card is charged – often on a recurring basis.

Because the first merchant “passes” the credit or debit card information to the second merchant, you may have no clue that you are actually paying for the service, until it shows up on your bill. It’s especially troublesome if you’ve used a debit card and the money has mysteriously disappeared from your bank account. And good luck trying to stop or reverse the charges.

The Committee staff report that came out of that hearing revealed just how lucrative this practice is. Three companies – Affinion, Vertrue and Webloyalty – had bilked 35 million consumers out of more than one billion dollars.

As of May 2, 1010, Visa has voluntarily agreed to stop its merchants from engaging in this practice. The only conceivable reason they allowed it in the first place had to have been the cut they took on those transactions.

Have you been stung by a merchant that passed your credit card information to someone else? Share your story in the comments section below.

Gerri Detweiler – Personal Finance Advisor for Credit.com, Gerri contributes budgeting, debt recovery and savings information online. She is also the co-author of Reduce Debt, Reduce Stress: Real Life Solutions for Solving Your Credit Crisis.