Eavesdropping

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.
Etymology.
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.
Techniques.
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 attacks.
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.<ref>