Surveillance Wp→ is the most common purpose. Simple surveillance simply involves showing up and taking notes. Surveillance of the leadership of an organization involves both long-term participation and being supportive and useful. The Communist Party USA was successfully infiltrated by the FBI during the Cold War with a substantial portion of the active members at its low point of 5,000 members being FBI informants including the functionaries who received funds from the Soviet government.
Other communist political tendencies sometimes engage in infiltration of revolutionary parties or organizations, both for surveillance and disruption and in order to gain control of their leadership. This is particularly true of organizations such as the Students for Democratic Society which have undefined goals and open membership.