Secret agents

Espionage (colloquially, spying) is the obtaining of secret or confidential information without the permission of the holder of the information. Spies help agencies uncover secret information. Any individual or spy ring (a cooperating group of spies), in the service of a government, company or independent operation, can commit espionage. The practice is clandestine, as it is by definition unwelcome and in many cases illegal and punishable by law. Espionage is a subset of "intelligence" gathering, which includes espionage as well as information gathering from public sources.

Espionage is often part of an institutional effort by a government or commercial concern. However, the term tends to associate with state spying on potential or actual enemies for military purposes. Spying involving corporations is known as industrial espionage.

One of the most effective ways to gather data and information about the enemy (or potential enemy) is by infiltrating the enemy's ranks. This is the job of the spy (espionage agent). Spies can return all sorts of information concerning the size and strength of enemy forces. They can also find dissidents within the enemy's forces and influence them to defect. In times of crisis, spies can also oblige to steal technology and sabotage the enemy in various ways. Counterintelligence operatives can feed false information to enemy spies, protecting important domestic secrets, and preventing attempts at subversion. Almost all nations have strict laws concerning espionage and the penalty for being caught is often severe. However, the benefits through espionage are often great enough that most governments and many large corporations make use of it to varying degrees.

...
Wikipedia