A spy is a person employed to obtain such secrets. Within the United States Intelligence Community, "asset" is a more common usage. A case officer, who may have diplomatic status (i.e., official cover or non-official cover) supports and directs the human collector. Cutouts are couriers who do not know the agent or case officer, but transfer messages. A safe house is a refuge for spies.
In larger networks the organization can be complex with many methods to avoid detection, including clandestine cell systems. Often the players have never met. Case officers are stationed in foreign countries to recruit and to supervise intelligence agents, who in turn spy on targets in their countries where they are assigned. A spy need not be a citizen of the target country. While the more common practice is to recruit a person already trusted with access to sensitive information, sometimes a person with a well-prepared synthetic identity, called a legend in tradecraft, may attempt to infiltrate a target organization.
These agents can be moles (who are recruited before they get access to secrets), defectors (who are recruited after they get access to secrets and leave their country) or defectors in place (who get access but do not leave).
Spies may also be used to spread disinformation in the organization in which they are planted, such as giving false reports about their country's military movements, or about a competing company's ability to bring a product to market. Spies may be given other roles that also require infiltration, such as sabotage.
Many governments routinely spy on their allies as well as their enemies, although they typically maintain a policy of not commenting on this. Governments also employ private companies to collect information on their behalf such as SCG International Risk and others.