Some people do not like being tracked on the net. DoubleClick adserver tracking cookies can do so. I got an alert from a-squared for mycomputername8adserver.02[1}.text Tracking Cookie (malware file).
But sometimes an opt out means opt-in through a flaw, and then you are hence-on tracked invisibly. Opt-out mechanisms are not always trustworthy, the adware man with spam attitudes. Read here: http://www.interhack.net/pubs/dc-proto-fail/. It is an old example and it may be fixed now, But it is only to demonstrate that nothing must be taken for granted (situation described 2000 P).
Watch your steps folks, trust no site until proven safe. Morale is sinking on the Net. And finally use a good updated hosts file. Saves you a lot of spying on your tracks,
I have doubleclick.net (.com and any other ones that I come accross) blocked for everything I can thing of from cookies, ads, images, etc. I think they are the absolute pits and very intrusive.
One thing someone once told me not to even press the No button and definitely never press the Yes button, whether this be for opting out or rejecting anything, use the X in the top right of the pop-up/window.
People feel safe and secure in clicking the No button without knowing what the processing is that happens on clicking NO. Clicking any button can launch any number of processes from downloading spyware/adware/malware or in the majority of cases a trustworthy web site just what it intimated it would do.
However, you never can be sure, there are some very devious people out there so it pays to be suspicious. and click the X at the top right corner of the window.