It's a standard practice for ad networks to resell cookies to advertisers. It's downright creepy.

You can make it stop a few ways:

- dump your cookies after each session. This is a pain and messes up a lot of stuff, so I don't do it.

- if you use chrome, there is a "don't track me" setting that helps tone this down a bit, but only a bit.

- you can click on the teeny little button at the top of these ads and follow the instructions to opt out.

Don't let the comments about being new to the internet bother you. Almost no one understands how ad networks and browsers interact, so you're in good company. I'm in this industry and I find it really creepy. The ad networks make it very hard to opt out because they charge a lot more for ads that make use of these tracking systems.