espionageThe practice of spying or using spies to obtain secret information.
Definitions:
The act of spying, especially a government spy obtaining secrets of another government.
betrayalAn act of deliberate disloyalty.
Definitions:
The act of betraying someone or something, or the fact of being betrayed.
double-crossAn act of betraying an ally, friend, or associate.
Definitions:
To deceive or betray (a person with whom one is supposedly cooperating).
infiltrateTo covertly enter or gain access to an organization or place to gather secret information or cause damage.
Definitions:
To enter or become established in gradually or surreptitiously, especially in order to acquire secret information.
treacheryAn act of betrayal; a violation of a person's trust or confidence.
Definitions:
Betrayal of trust; deceptive action or nature.