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Eavesdropping is the act of secretly or stealthily listening to the private conversation or communications of others without their consent in order to gather information. The practice is widely regarded as unethical, and in many jurisdictions is illegal.
The verb eavesdrop is a back-formation from the noun eavesdropper ("a person who eavesdrops"), which was formed from the related noun eavesdrop ("the dripping of water from the eaves of a house; the ground on which such water falls").
An eavesdropper was someone who would hang from the eave of a building so as to hear what is said within. The PBS documentaries Inside the Court of Henry VIII (April 8, 2015) and Secrets of Henry VIII’s Palace (June 30, 2013) include segments that display and discuss "eavedrops", carved wooden figures Henry VIII had built into the eaves (overhanging edges of the beams in the ceiling) of Hampton Court to discourage unwanted gossip or dissension from the King's wishes and rule, to foment paranoia and fear, and demonstrate that everything said there was being overheard; literally, that the walls had ears.
Eavesdropping vectors include telephone lines, cellular networks, email, and other methods of private instant messaging. VoIP communications software is also vulnerable to electronic eavesdropping via infections such as trojans.
Network eavesdropping, also known as eavesdropping attack, sniffing attack, or snooping attack, is a method that retrieves user’s information through the internet. Network eavesdropping is a network layer attack that focuses on capturing small packets from the network transmitted by other computers and reading the data content in search of any type of information. This type of network attack is generally one of the most effective as a lack of encryption services are used. It is also linked to the collection of metadata. Those who perform this type of attack are generally black-hat hackers; however, government agencies, such as the National Security Agency, have also been connected.
It happens on electronic devices such as a computer and a smartphone. This network attack typically happens under the usage of unsecured networks, such as public wifi connections or shared electronic devices. Eavesdropping attacks through the network is considered one of the most urgent threats in industries that rely on collecting and storing data. 
The threat of network eavesdroppers is a growing concern. Research and discussions are brought up in the public's eye, for instance, types of eavesdropping, open-source tools, and commercial tools to prevent eavesdropping. Models against network eavesdropping attempts are built and developed as privacy is increasingly valued. Sections on cases of successful network eavesdropping attempts and its laws and policies in the National Security Agency are mentioned. Some laws include the Electronic Communications Privacy Act and the Foreign Intelligence Surveillance Act.
- Cellphone surveillance
- Computer surveillance
- Fiber tapping
- Katz v. United States (1967)
- Global surveillance disclosures (2013–present)
- Keystroke logging
- Magic (cryptography)
- Man-in-the-middle attack
- Mass surveillance
- NSA warrantless surveillance controversy (December 2005 – 2006)
- Opportunistic encryption
- Party line
- People watching
- Secure communication
- Telephone tapping
- Covert listening device
- Bighash, Leila, Kristen S. Alexander, Christina S. Hagen, Andrea B. Hollingshead. 2020. "A Model of Social Eavesdropping in Communication Networks". International journal of communication Online: 3704.
- "eavesdrop – Definition of eavesdrop in English by Oxford Dictionaries". Oxford Dictionaries – English.
- Inside the Court of Henry VIII. Public Broadcasting Service. April 8, 2016.
- Stollznow, Karen (August 7, 2014). "Eavesdropping: etymology, meaning, and some creepy little statues". KarenStollznow.com.
- Garner, p. 550[full citation needed]
- "TeamMentor 3.5". vulnerabilities.teammentor.net. Retrieved 2019-09-27.
- Li, Xuran; Wang, Qiu; Dai, Hong-Ning; Wang, Hao (2018-06-14). "A Novel Friendly Jamming Scheme in Industrial Crowdsensing Networks against Eavesdropping Attack". Sensors. 18 (6): 1938. doi:10.3390/s18061938. ISSN 1424-8220.