Star Trek's Section 31 used to be Starfleet's darkest secret, but many of their most evil deeds are now a matter of public record. A covert intelligence agency tasked with protecting the Federation no matter the cost, Section 31 has been responsible for attempted genocide, and incitement of war, and has even stooped to robbing the graves of some Starfleet legends. Their existence was uncovered by Doctor Julian Bashir (Alexander Siddig) in Star Trek: Deep Space Nine, when Section 31 attempted to recruit DS9's genetically enhanced physician. Later Star Trek canon revealed that Section 31 has been part of Starfleet from before the founding of the Federation.

https://screenrant.com/star-trek-section-31-evil-things/