Even more sophisticated technology permits the Government to intercept any telephone, telegram, or telex communication which is transmitted at least partially through the air, as most such communications now are. This type of interception is virtually undetectable and does not require the cooperation of private communications companies. Techniques such as these have been used, and continue to be used, by intelligence agencies in their intelligence operations.
Since the early part of this century the FBI has utilized wiretapping and “bugging” techniques in both criminal and intelligence investigations. In a single year alone (1945), the Bureau conducted 519 wiretaps and 186 microphone surveillances (excluding those conducted by means of microphones planted on informants).
Until 1972, the Bureau used wiretaps and bugs against both American citizens and foreigners within the United States — without judicial warrant — to collect foreign intelligence, intelligence and counterintelligence information, to monitor “subversive” and violent activity, and to determine the sources of leaks of classified information. The FBI still uses these techniques without a warrant in foreign intelligence and counterintelligence investigations.