(covers information from several alternate timelines)
Starfleet Security was an agency in Starfleet. This agency was one of the oldest with its origins dating back to the United Earth Starfleet. The agency was located at Fleet Operations Center in San Francisco, Earth, Sol Sector. The agency was responsible for safeguarding the Federation from internal and external threats, for conducting criminal investigations, and for guarding Federation facilities. (ENT: "Demons", directories)
That same year, the dedication plaque of the Columbia NX-02 listed the names of notable officers assigned to this agency who protected the shipyard where the starship was constructed and tested. (ENT: "Affliction", Columbia dedication plaque)
- L. Ward (previously worked on Columbia)
- S. D'Errico (previously worked on Columbia)
In the 2350s, a secret group at Starfleet Security engaged in an illegal operation to develop a Starfleet phasing cloaking device, in direct violation of the Treaty of Algeron. The phasing cloak was tested aboard the USS Pegasus in 2358, under the command of Captain Erik Pressman, but ended in disaster when it appeared the Pegasus was destroyed. The entire affair was subsequently covered up by Starfleet Intelligence. Twelve years later, the Chief of Starfleet Security at the time, Admiral Raner, oversaw an operation to retrieve the experimental cloaking device. (ENT: "These Are the Voyages..."; TNG: "The Pegasus")
In 2367, Vice Admiral Thomas Henry, who was attached to Starfleet Security, boarded the USS Enterprise NCC-1701-D to observe a hearing overseen by former Starfleet admiral Norah Satie, concerning an attempt to uncover a supposed conspiracy at the heart of Starfleet. (TNG: "The Drumhead")
In 2371, due to skepticism related to Constable Odo's abilities as security chief, Starfleet Security assigned Lieutenant Commander Michael Eddington to Deep Space 9, to oversee security issues pertaining to Starfleet matters. (DS9: "The Search, Part I")
Starfleet Security had documented several incidents of Cardassians being surgically altered with the purpose of infilitrating an enemy. It was determined by the USS Voyager crew that Seska was another of these incidents – surgically altered as a Bajoran, she infilitrated the Maquis. (VOY: "State of Flux")
In 2372, Admiral Leyton made Benjamin Sisko acting head of Starfleet Security, in face of the apparent Changeling infiltration of Starfleet. In this capacity, Sisko discovered that Leyton was using the recent bombing of the Antwerp Conference as an excuse to attempt to seize power by the military, by instilling paranoia about the threat posed by the Dominion. Sisko subsequently uncovered Leyton's conspiracy, forcing him to resign, and returned to Deep Space Nine. (DS9: "Homefront", "Paradise Lost")
- Malcolm Reed was posted as armory officer - prior to the Federation Starfleet Security being established - aboard the Enterprise.
- One of Hikaru Sulu's assignments aboard the USS Enterprise from 2265 through 2270 was that of Security officer.
- Pavel Chekov was in charge of security on the USS Enterprise-A in 2293.
- Tasha Yar served as security officer aboard the USS Enterprise-D.
- Worf served as security officer aboard the USS Enterprise-D after Yar's death.
- Odo performed station security on Deep Space 9, although he was not part of Starfleet Security.
- Michael Eddington was responsible for Starfleet security on Deep Space 9 and the USS Defiant in 2371 and 2372.
- Aboard the USS Voyager, Tuvok was the security officer.