A recent report from the U.S. Senate says hundreds of online retailers have added marketing come-ons to their transactions that have bilked consumers out of more that $1 billion.

Here's how it works: Right after a customer makes a purchase, a screen pops up offering cash back on their next purchase.

Sometimes it looks like a coupon, sometimes it's offered through eye-catching text highlighted in bold red or blue.

But customers who click on the offer are actually enrolling in membership clubs such as Affinion, Vertrue and Webloyalty.

While they do provide discounts, the come-ons are so misleading that customers rarely realize they've signed up.

Of course, that doesn't stop the clubs from dinging the customer's credit card for $10 to $19.95 a month until he or she notices the charge on their bill and complains.

How do the membership clubs obtain the card number, expiration date and security code? From the retailer where the customer just made the purchase.

This isn't something that only disreputable online retailers are doing.

Senate investigators found that more than 450 sites, including such big names as Barnes & Noble, Pizza Hut, Victoria's Secret and US Airways, are working with the clubs -- and splitting the profits.