Evidon helps you understand how companies collect and use your data—often to target ads to you—and gives you the ability to opt out of targeting if you wish. When you opt out of a company through an Evidon web page, Evidon sends a message to that company's servers. This message requests that an opt-out cookie be returned from the servers and stored on your computer in the form of a browser cookie
Most web browsers allow you to view the contents of the cookies that it has stored on your computer. This allows you to check for the presence of the opt out cookies yourself. For example, here is what Firefox shows for DoubleClick's opt-out cookie:
To see a particular company's opt out cookie's contents, go to this page, search for the company you are looking for, and click on its name. If that company provides an opt out, then you'll see the opt-out cookie information under the 'Opt-out cookies' section.
It's important to realize that cookies are not shared across web browsers. For example, Internet Explorer and Firefox each store cookies in different locations, and they cannot read each others' cookies. Therefore, if you opt out of tracking by Company ABC in Internet Explorer, you have NOT opted out of tracking by Company ABC in Firefox. You will need to repeat the process in Firefox in order to opt out in both browsers.