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Eavesdropping is the act of secretly listening to the private conversation of others without their consent, as defined by Black's Law Dictionary
Black's Law Dictionary
Black's Law Dictionary is the most widely used law dictionary in the United States. It was founded by Henry Campbell Black. It is the reference of choice for definitions in legal briefs and court opinions and has been cited as a secondary legal authority in many U.S...

. This is commonly thought to be unethical and there is an old adage
An adage is a short but memorable saying which holds some important fact of experience that is considered true by many people, or that has gained some credibility through its long use....

 that "eavesdroppers seldom hear anything good of themselves...eavesdroppers always try to listen to matters that concern them."


Ancient Anglo-Saxon law
Anglo-Saxon law
Anglo-Saxon law is a body of written rules and customs that were in place during the Anglo-Saxon period in England, before the Norman conquest. This body of law, along with early Scandinavian law and continental Germanic law, descended from a family of ancient Germanic custom and legal thought...

 punished eavesdroppers, who skulked in the eavesdrip
The eavesdrip is the width of ground around a house or building which receives the rain water dropping from the eaves.This is sometimes also known as the eavesdrop, but an eavesdrop is also a small, not very visible hole in a building used to listen in on the conversation of people awaiting...

 of another's home, with a fine; the eavesdropper was also sometimes called the eavesdrop. Eavesdrop also means a small low visibility hole near the entrance to a building (generally under the eaves
The eaves of a roof are its lower edges. They usually project beyond the walls of the building to carry rain water away.-Etymology:"Eaves" is derived from Old English and is both the singular and plural form of the word.- Function :...

) which would allow the occupants to listen in on the conversation of people awaiting admission to the house. Typically this would allow the occupant to be prepared for unfriendly visitors.

Early telephone
The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...

 systems shared party lines
Party line (telephony)
In twentieth-century telephone systems, a party line is an arrangement in which two or more customers are connected directly to the same local loop. Prior to World War II in the United States, party lines were the primary way residential subscribers acquired local telephone service...

 which would allow the sharing subscribers to listen to each others' conversations. This was a common practice in rural America which resulted in many incidents and feuds.


Eavesdropping can also be done over telephone
The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...

 lines (wiretapping), email
Electronic mail, commonly known as email or e-mail, is a method of exchanging digital messages from an author to one or more recipients. Modern email operates across the Internet or other computer networks. Some early email systems required that the author and the recipient both be online at the...

, instant messaging
Instant messaging
Instant Messaging is a form of real-time direct text-based chatting communication in push mode between two or more people using personal computers or other devices, along with shared clients. The user's text is conveyed over a network, such as the Internet...

, and other methods of communication
Communication is the activity of conveying meaningful information. Communication requires a sender, a message, and an intended recipient, although the receiver need not be present or aware of the sender's intent to communicate at the time of communication; thus communication can occur across vast...

 considered private. (If a message is publicly broadcast, witnessing it is not considered eavesdropping.) VoIP communications software is also vulnerable to electronic eavesdropping via malware infections such as Trojan.


The verb eavesdrop was originally a back-formation
In etymology, back-formation is the process of creating a new lexeme, usually by removing actual or supposed affixes. The resulting neologism is called a back-formation, a term coined by James Murray in 1889...

 of the noun eavesdropper ("a person who eavesdrops") which was formed from the unrelated noun eavesdrop ("the dripping of water from the eaves of a house; the ground on which such water falls"). An eavesdropper was one who stood at the eavesdrop (where the water fell, ie near the house) so as to overhear what was said inside.

See also

  • Computer surveillance
    Computer surveillance
    Computer surveillance is the act of performing surveillance of computer activity, and of data stored on a hard drive or being transferred over the Internet....

    ECHELON is a name used in global media and in popular culture to describe a signals intelligence collection and analysis network operated on behalf of the five signatory states to the UK–USA Security Agreement...

  • Espionage
    Espionage or spying involves an individual obtaining information that is considered secret or confidential without the permission of the holder of the information. Espionage is inherently clandestine, lest the legitimate holder of the information change plans or take other countermeasures once it...

  • Fiber tapping
    Fiber tapping
    Fiber tapping is a method to extract signal from an optical fibre without breaking the connection. Tapping of optical fibre allows diverting some of the signal being transmitted in the core of the fibre into another fibre or a detector...

  • Katz v. United States
    Katz v. United States
    Katz v. United States, , is a United States Supreme Court case discussing the nature of the "right to privacy" and the legal definition of a "search." The Court’s ruling adjusted previous interpretations of the unreasonable search and seizure clause of the Fourth Amendment to count immaterial...

  • Keystroke logging
    Keystroke logging
    Keystroke logging is the action of tracking the keys struck on a keyboard, typically in a covert manner so that the person using the keyboard is unaware that their actions are being monitored...

  • Magic (cryptography)
    Magic (cryptography)
    Magic was an Allied cryptanalysis project during World War II. It involved the United States Army's Signals Intelligence Section and the United States Navy's Communication Special Unit. -Codebreaking:...

  • Man-in-the-middle attack
    Man-in-the-middle attack
    In cryptography, the man-in-the-middle attack , bucket-brigade attack, or sometimes Janus attack, is a form of active eavesdropping in which the attacker makes independent connections with the victims and relays messages between them, making them believe that they are talking directly to each other...

  • NSA warrantless surveillance controversy
    NSA warrantless surveillance controversy
    The NSA warrantless surveillance controversy concerns surveillance of persons within the United States during the collection of foreign intelligence by the U.S. National Security Agency as part of the war on terror...

     (December 2005-2006)
  • Opportunistic encryption
    Opportunistic encryption
    Opportunistic Encryption refers to any system that, when connecting to another system, attempts to encrypt the communications channel otherwise falling back to unencrypted communications. This method requires no pre-arrangement between the two systems.Opportunistic encryption can be used to...

  • Privacy
    Privacy is the ability of an individual or group to seclude themselves or information about themselves and thereby reveal themselves selectively...

  • Secure communication
    Secure communication
    When two entities are communicating and do not want a third party to listen in, they need to communicate in a way not susceptible to eavesdropping or interception. This is known as communicating in a secure manner or secure communication...

  • Surveillance
    Surveillance is the monitoring of the behavior, activities, or other changing information, usually of people. It is sometimes done in a surreptitious manner...

  • Telephone tapping
    Telephone tapping
    Telephone tapping is the monitoring of telephone and Internet conversations by a third party, often by covert means. The wire tap received its name because, historically, the monitoring connection was an actual electrical tap on the telephone line...

  • Ultra
    Ultra was the designation adopted by British military intelligence in June 1941 for wartime signals intelligence obtained by "breaking" high-level encrypted enemy radio and teleprinter communications at the Government Code and Cypher School at Bletchley Park. "Ultra" eventually became the standard...