Buying things on the Internet just got a little safer, thanks to an aggressive move by Visa (NYSE:V). Today, Visa announced that they have shut down the credit card processing for 100 merchants who used aggressive tactics to bill cardholders on the Internet. The merchants all engaged in a practice called “negative option” in their credit and debit card billing.

The merchants that were shut down included merchants that sold products on a continuity basis (where shoppers allegedly agreed to pay a monthly fee for a product) and where the shoppers “opted in” to the monthly fee in a “negative option”. Here’s an example of one of the practices (if you’ve spent any time on the Internet, you’ve seen these ads).

A shopper sees an ad for a “free trial” of a diet product (usually featuring Acai berry or something similar). The shopper provides their shipping and contact information to receive the “free” bottle of diet pills, and then is taken to a checkout page to complete the order. The order page asks for the shoppers credit or debit card number (ostensibly to pay for a nominal shipping charge). Once the credit or debit card number is submitted, some fine print may be displayed to the shopper telling them that unless the “free trial” is canceled within a short period of time, the shopper authorizes the merchant to continue to charge their credit or debit card each month. Most shoppers don’t see the fine print, and then are surprised when their credit or debit card bill has a charge for $5, $10, $50 or more each month.

This is called a “negative option” because the billing continues until the cardholder cancels the subscription. The problem is that the unscrupulous merchants didn’t always make it clear to the customers that they were even entering into a subscription.

Visa’s steps to shut down these aggressive merchants makes the Internet a bit safer for users of credit and debit cards.

Here’s what Visa had to say about the move:

“We’ve been monitoring this situation from this past summer in particular,” said William M. Sheedy, a Visa group president. The number of complaints from cardholders who disputed ongoing charges they never agreed to shot up, although the merchants and the products they sold often varied.

While there are always a handful of complaints about merchants, most are resolved quickly. But in the case of the ongoing charges, it was clear the problem was widespread. “Consumers are being fleeced,” Sheedy said.

Visa told The Associated Press that about 100 merchants had their payment processing terminated because of chronic complaints since early summer. The scam is so common, the San Francisco payment processor is teaming up with the Federal Trade Commission and the Better Business Bureau to alert consumers.

Great move, Visa!