Political surveillance is used to get information about groups and individuals who are considered a potential threat to public order or security, such as ethnic and religious minorities, political activists, dissidents and foreigners. It includes the building up of political dossiers, wire-tapping, burglary, censorship and intimidation; and may be aided by the political appointment of supporters to key positions. Political espionage may be used during elections or to achieve indoctrination at other times. It serves particularly to tighten government control and to promote the interests of an elite. It can serve political repression and may be used to incriminate opponents in either constitutional or totalitarian systems. Acts of corruption and other injustices may be effectively covered up by intelligence activities.