user-tracking

If a given web server can only read cookies from those set within its own domain, how do Internet advertisers track user's web traffic from websites outside of their network? Is there some kind of " supercookie " global advertising system that allows advertisers to retrieve upper-level domain cookies and then query some server (from an affiliate) that houses information about where that user has been? Update: To clarify my question, is it possible for an advertiser that publishes ads on "example2.com" to ascertain that I visited a particular site "example1.com" if they had never served an ad

We have several websites on different domains and I'd like to be able to track users' movements on these sites. Obviously cookies are not feasable, because they don't cross domain borders. I could look at a combination of IP address and User Agent, but there are some cases where that does not work. I don't want to use flash or other plugins. Any ideas? Or am I doomed to rely on the IP/User_Agent combination? You can designate one domain or subdomain to tracking and have it serve a 1x1 pixel image which you include in all pages you would like to track. Serve a cookie with the image, look at the

It is impossible to identify a user or request as unique since duping is trivial. However, there are a handful of methods that, combined, can hamper cheating attempts and give a user quasi-unique status. I know of the following: IP Address - store the IP address of each visitor in a database of some sort Can be faked Multiple computers/users can have the same address Users with dynamic IP addresses (some ISP issue them) Cookie tracking - store a cookie per visitor. Visitors that don't have it are considered "unique" Can be faked Cookies can be blocked or cleared via browser Are there more ways