A method for tracking information about the activities of users of a social networking system while on another domain, the method comprising: maintaining a profile for each of one or more users of the social networking system, each profile identifying a connection to one or more other users of the social networking system and including information about the user (1030, 1040); tracking actions taken by one or more of the users of the social networking system on third-party websites by: receiving a tracking pixel message generated by a client application associated with the one or more users of the social networking system, when the one or more users (1030, 1040) of the social networking system take an action on a third-party website having a different domain than the social network system, wherein the tracking pixel message communicating the action taken by the one or more users (1030, 1040) of the social networking system on the third-party website; validating the tracking pixel message by validating a tracking identifier of the tracking pixel message using a hash value; identifying a user (1030, 1040) of the social networking system associated with the tracking pixel message by accessing a user identifier associated with the tracking pixel message, the user identifier corresponding to the user; recording, for each validated tracking pixel message, the action taken by the user on the third-party website in a pixel-user association table; correlating each of the actions on the third-party website recorded in the pixel-user association table with one or more advertisements presented to the one or more users (1030, 1040) of the social networking system; and generating a tracking report for display to an advertiser associated with the one or more advertisements, the tracking report comprising statistical data that associates one or more user profile attributes to one or more of the advertisements and actions on the third-party website that correlate to respective ones of the advertisements. maintaining a profile for each of one or more users of the social networking system, each profile identifying a connection to one or more other users of the social networking system and including information about the user (1030, 1040); tracking actions taken by one or more of the users of the social networking system on third-party websites by: receiving a tracking pixel message generated by a client application associated with the one or more users of the social networking system, when the one or more users (1030, 1040) of the social networking system take an action on a third-party website having a different domain than the social network system, wherein the tracking pixel message communicating the action taken by the one or more users (1030, 1040) of the social networking system on the third-party website; validating the tracking pixel message by validating a tracking identifier of the tracking pixel message using a hash value; identifying a user (1030, 1040) of the social networking system associated with the tracking pixel message by accessing a user identifier associated with the tracking pixel message, the user identifier corresponding to the user; recording, for each validated tracking pixel message, the action taken by the user on the third-party website in a pixel-user association table; correlating each of the actions on the third-party website recorded in the pixel-user association table with one or more advertisements presented to the one or more users (1030, 1040) of the social networking system; and generating a tracking report for display to an advertiser associated with the one or more advertisements, the tracking report comprising statistical data that associates one or more user profile attributes to one or more of the advertisements and actions on the third-party website that correlate to respective ones of the advertisements. receiving a tracking pixel message generated by a client application associated with the one or more users of the social networking system, when the one or more users (1030, 1040) of the social networking system take an action on a third-party website having a different domain than the social network system, wherein the tracking pixel message communicating the action taken by the one or more users (1030, 1040) of the social networking system on the third-party website; validating the tracking pixel message by validating a tracking identifier of the tracking pixel message using a hash value; identifying a user (1030, 1040) of the social networking system associated with the tracking pixel message by accessing a user identifier associated with the tracking pixel message, the user identifier corresponding to the user; recording, for each validated tracking pixel message, the action taken by the user on the third-party website in a pixel-user association table; correlating each of the actions on the third-party website recorded in the pixel-user association table with one or more advertisements presented to the one or more users (1030, 1040) of the social networking system; and generating a tracking report for display to an advertiser associated with the one or more advertisements, the tracking report comprising statistical data that associates one or more user profile attributes to one or more of the advertisements and actions on the third-party website that correlate to respective ones of the advertisements.