Floodlight conversion tracking
Floodlight recognizes users by their DoubleClick cookie. A cookie is a small text file. It consists of an ID number that is associated with a computer and browser. DoubleClick writes a cookie to a user's browser the first time a user visits a website that uses DoubleClick technology, and accesses the cookie on every subsequent occasion when that user interacts with a website using DoubleClick technology.
Once the cookie is set, the ad server records the cookie ID each time a user is served an ad (recorded as an impression in DFA), clicks on an ad, or visits a webpage containing a Floodlight tag. In this way, the activity of a given user can be tracked.
Keep in mind that cookies are associated with browsers, not people. If a family of four shares a computer, the activity associated with one cookie might be the result four different people surfing the web. Similarly, if one person uses two different browsers on the same computer, there's usually a separate DoubleClick cookie for each browser. So if someone views your ad in Firefox, then visits your website in Safari, Floodlight will have no way of associating the ad impression with the visit to the Floodlight page, even though both events took place on the same computer. And for people who use more than one computer, there's no way to associate their actions on one machine with their actions on another.
That said, most people mostly use just one or two browsers and one or two computers most of the time. Despite its limitations, Floodlight has plenty of useful data to work with and is still a powerful tool for helping you to understand the effectiveness of your campaigns.