The ads look like the image to the right. You see them immediately after you pay for a legitimate product from a legitimate company.

They now have your credit card number, and if you click the button to enroll, they will take you to a target that looks something like this:
https://ad.doubleclick.net/jump/N3446.Meadwestvaco.com/B3340789;q=F0B090B0B05CC5C5855554BC0676EC94D5A 5349544946DB6A69D0445A56524340E410212C7E72773A 7F774C6A542661604D3D5D566B5B4C7C653AF26660726;
They will use your credit card number to enroll you in their program for which you will pay a recurring monthly fee.
They go by several different names, which makes it harder to spot the charge on your charge card bill.
Beware. Either read the fine print (which will make you turn it down) or better yet, don’t click on it. Your charge card company will view it as a legitimate charge that you agreed to. The only remuneration will be up to three month’s refund from this scam company (not from your credit card company), and sometimes only if you’re painful on the phone.
Tell them you want both cancellation and a full refund. Also ask them what other names they go by. They will tell you. Write them down, and be on the lookout for all such names on your credit card in the future.
The frustrating part is that the company, Doubleclick, is owned by Google. The image example above appeared with a purchase from At-A-Glance (a company that makes calendars).
Is Google participating in click fraud?