The Trojan Horse Project was a research project concerning holographic infiltration for purposes of reconnaissance commissioned by Starfleet Intelligence. The project was in development in the 2370s aboard Jupiter Station by Dr. Lewis Zimmerman. One avenue of research was the use a holographic fly, named Roy, as a micro-surveillance spy.
In 2376, while suffering from a seemingly fatal disease, Dr. Zimmerman recorded a last will and testament whereby he bequeathed the project to Reginald Barclay, the only person he trusted to complete it, although he later recovered from the disease. (VOY: "Life Line")