Rankings are based on audience measurement on U.S. Internet household population. A property is defined as a consolidation of multiple domains and URLs owned by a single entity.
Unique audience is a measure of the total number of individuals that visit a property.
An impression is counted each time an ad banner is fully loaded onto a user's screen. Microsoft 797,902,513 33.75 2. Amazon 176,327,444 33.82 5. ClassMates 102,891,345 17.81 7. America Online 100,754,161 19.39 8.