Quoting the Patent Application:

"In one embodiment, a method is described for tracking information about the activities of users of a social networking system while on another domain. The method includes 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. The method additionally includes receiving one or more communications from a third-party website having a different domain than the social network system, each message communicating an action taken by a user of the social networking system on the third-party website. The method additionally includes logging the actions taken on the third-party website in the social networking system, each logged action including information about the action."