An online system transmits third-party content originating from a third-party system to a client device. The third-party content includes a pointer to a third-party application associated with the third-party system. When the client device receives an interaction with the third-party content from a user of the client device, the client device executes the third-party application and generates an attribution identifier from which the user's identity cannot be determined. The attribution identifier is transmitted to the online system. Subsequently, the client device determines information describing interactions by the user with the third-party application that is transmitted to the third-party system along with the attribution identifier. The third-party system transmits the attribution identifier and the information describing interaction with the third-party application to the online system, which matches the attribution identifiers to associate the interaction with the third-party content with the interactions with the third-party application.