From the Church/Tower hearings on COINTELPRO and other illegal operations and violations of civil rights:
Groups and individuals have been harassed and disrupted because of their political views and their lifestyles. Investigations have been based upon vague standards whose breadth made excessive collection inevitable. Unsavory and vicious tactics have been employed–including anonymous attempts to break up marriages, break up meetings, ostracize persons from their professionals, and provoke target groups into rivalries that might result in deaths. Intelligence agencies have served the political and personal objectives of presidents and other high officials. While the agencies often committed excesses in response to pressure from high officials in the Executive branch and Congress, they also occasionally initiated improper activities on their own and then concealed them from officials whom they had a duty to inform.
1 Book II: Intelligence Activities and the Rights of Americans, page 5