Network Advertising Initiative (NAI)
The NAI offers a centralized opt-out to avoid some types of tracking of their web activities. Some online ads appear on multiple web sites, network ads. If you browse with cookies turned on (as many people do) at a couple or more of web sites with network ads, or make some purchases or register at those sites, then your activities may in some situations be tracked. In some cases, things you do online can be linked back to you personally by name or email address and then merged with other information about you.
If you opt-out of NAI tracking, it means that companies that have tracking ads at multiple web sites will no longer assemble a file of all of the places you have visited, will no longer link your web activities with you personally, and will no longer merge the web activities connected with their ads with other information about you.
The NAI opt-out uses what is called an "opt-out cookie" to tell advertisers not to track you. For more information: NAI Frequently Asked Questions Page.
How to opt-out
Open your web browser and check the cookie settings to accept all cookies. Go to http://networkadvertising.org/consumer/opt_out.asp and click the Consumer opt-out button. You will see an opt-out page listing network advertisers with checkboxes to check and uncheck. If the page did not automatically opt you out of everything you wanted to opt-out of, you can follow the individual links listed under each advertiser on the NAI opt-out page. After you have opted out, if you must keep the opt-out cookies on your computer.