While there's not a lot to go on in the question, one possible match is Vernor Vinge's A Deepness in the Sky. In this two fleets of spaceships arrive at the same planet, inhabited by a Spiderlike race of sentient beings.
After thousands of years searching, humans stand on the verge of first contact with an alien race. Two human groups: the Qeng Ho, a culture of free traders, and the Emergents, a ruthless society based on the technological enslavement of minds.
After the Emergents take control of the Qeng Ho fleet, Pham Nuwen organises a small resistance to fight back. Pham Nuwen is really old, having been kept alive though cold-sleep and relativistic travel and knows back-door entries to the Qeng Ho fleet's technology using older legacy code functions and physical capabilities of some of the fleet's technology, that were never revealed to the general users when the technology was bought, that Pham Nuwen only knows about because he arranged the purchase.