In Greek mythology, the Trojan horse was a hollow wooden horse used by Greek soldiers during a war to enter the city of Troy. Metaphorically, a Trojan horse was a person or thing intended to trick or deceive another, such as an enemy or opponent, and bringing about their downfall from within a secure location.
In 2257, Philippa Georgiou stated that if Gabrielle Burnham was a Trojan horse, then the USS Discovery's defenses would prove woefully inadequate. (DIS: "Perpetual Infinity")