Impersonating a Starfleet officer

The crime of impersonating a Starfleet officer was the act of falsely presenting oneself as a Starfleet officer and using this pretense to falsely act in the name of the service. A person committed this offense by such actions as wearing a Starfleet uniform to deceive others into believing they were a Starfleet officer, issuing orders to legitimate Starfleet personnel, or falsely conducting activities in the name of Starfleet.

In 2151, a time traveler from the 31st century, infiltrated the Enterprise NX-01, posing as a steward named Crewman Daniels for the first few weeks of the ship's voyage. (ENT: "Cold Front")

In 2266, the last surviving M-113 creature assumed the appearance of USS Enterprise crew members Green and Leonard McCoy while stalking various crew members to consume the salt in their bodies. (TOS: "The Man Trap")

In 2268, the android Norman posed as a sciences division lieutenant in order to gain control of the USS Enterprise and divert it to the planet Mudd per Harry Mudd's orders. He was able to pass as a Human primarily because he avoided his required physical. (TOS: "I, Mudd")

In 2368, a Satarran using the alias of Kieran MacDuff posed as the executive officer of the USS Enterprise-D as part of an attempt to use the starship to destroy the Lysian Central Command. (TNG: "Conundrum")

In 2370, William Samuels impersonated a Starfleet officer on Deep Space 9 in order for him to destroy the Cardassian freighter the Bok'Nor, which was docked at the station, for the Maquis. (DS9: "The Maquis, Part I")

In 2371, The Doctor experienced a delusion due to a kinoplasmic radiation surge. Told by Reginald Barclay that he was actually Lewis Zimmerman, and USS Voyager was a holographic simulation, The Doctor accused Barclay of being an alien impersonating a Starfleet officer. (VOY: "Projections")

During the Dominion cold war, various Changelings used their shape-shifting abilities to impersonate Starfleet personnel at key facilities. one Changeling briefly impersonated Doctor Julian Bashir aboard the USS Defiant in 2371 as part of an unsuccessful attempt to incite a war between the United Federation of Planets and the Tzenkethi. (DS9: "The Adversary") Two Changeling (possibly the same one) assumed the appearances of Vice Admiral Leyton and Chief Miles O'Brien at Starfleet Headquarters on Earth in 2372. The former Changeling claimed there were four of his kind on Earth at the time, not counting Odo. (DS9: "Homefront", "Paradise Lost") Another Changeling also posed as Bashir at Deep Space 9 in 2373, this time, apparently, for as long as four weeks. (DS9: "In Purgatory's Shadow", "By Inferno's Light")

In 2375, the genetically-engineered Humans Jack, Patrick, and Lauren were all charged with impersonating Starfleet officers after they brought Sarina Douglas to Deep Space 9, during which they wore Starfleet uniforms and ordered others such as Nog to contact Julian Bashir. Patrick was dressed as an admiral, Jack as an operations officer, and Lauren as a science officer. Whenever they were questioned about their activities, Patrick answered "That's a stupid question!", which succeeded in continuing the deception. Because they were only trying to get assistance for Sarina, Bashir convinced Benjamin Sisko to ask that the charges be dropped. (DS9: "Chrysalis")

The following year, the crew of the USS Voyager discovered con artists Dala, Mobar, and Zar impersonating Voyager officers Kathryn Janeway, Tuvok, and Chakotay, respectively. They were able to do so after deceiving Neelix and Tom Paris into allowing them onto the Delta Flyer where they stole their database and acquired the knowledge of Starfleet within it. They then used this information to impersonate the aforementioned officers and swindle unsuspecting victims. After being captured by the Voyager crew, they were turned over to local authorities for prosecution. (VOY: "Live Fast and Prosper")

In 2383, a Vau N'Akat member of The Order known only as "The Vindicator" had joined Starfleet disguised as Trill Ensign Asencia. She was stationed on the USS Dauntless and smuggled her Drednok unit aboard, keeping it disguised as a table in her quarters. When the Dauntless recovered The Diviner from Tars Lamora, the Vindicator was able to restore his lost memories and enlist his aid. (PRO: "Masquerade") Vice Admiral Kathryn Janeway walked in on them and "Asencia" knocked her unconscious with a phaser stun. Dal R'El of the USS Protostar attempted to contact Janeway telepathically while the two ships exchanged fire, resulting in him accidentally swapping bodies with her. Dal was forced to impersonate Janeway for a while until the procedure could be reversed, but his unusual behavior led the Dauntless crew to imprison Janeway in the brig until she could explain the situation. (PRO: "Mindwalk") After Dauntless intercepted the Protostar, the Vindicator beamed aboard and activated a subspace broadcast, allowing the living construct to force all Starfleet ships within range to fire on each other, before escaping into space. (PRO: "Supernova, Part 1")

In 2401, a rogue Changeling murdered and impersonated Ensign Eli Foster of the USS Titan-A and intentionally damaged the ship's warp drive when the Shrike attacked it in the Ryton Nebula. This changeling was killed by Commander Seven of Nine while attempting further sabotage. Commander Ro Laren of Starfleet Security learned these changelings had infiltrated Starfleet to the highest levels and were virtually undetectable. She was able to alert Jean-Luc Picard aboard the Titan-A before being assassinated by Changeling moles posing the crew of the USS Intrepid. (PIC: "Seventeen Seconds", "No Win Scenario", "Imposters") Captain Vadic of the Shrike impersonated a member of the Starfleet security team that apprehended William T. Riker on Daystrom Station, violently interrogating him before murdering the other members of her security detail and taking him to her ship. (PIC: "The Bounty") Picard and the Titan-A crew soon learned Captain Tuvok, possibly others at Starfleet Command were compromised as well. (PIC: "Dominion")