Starfleet Security was a branch of Starfleet responsible for safeguarding the Federation from outside threats, and for conducting criminal investigations.
22nd century
Harris was a member of Starfleet Security until 2149, at which point he became a member of the covert operations group known as Section 31.
In 2154, Commander Collins was an officer in Starfleet Security. When Doctor Phlox was abducted in San Francisco as part of a Klingon plot, she was in charge
of the investigation.
24th century
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.
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.
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.
