Ethical subroutines are a programmatic method to describe the characteristics by which artificial lifeforms, like Lieutenant Commander Data or Lore; and holograms, like The Doctor, determine what is ethically right and wrong. (TNG: "Datalore"; VOY: "Equinox, Part II"; Star Trek: Insurrection)
In 2369, Lore disabled Data's ethical subroutines and made him perform dangerous experiments on the Borg and Geordi La Forge. With no moral obligation to his friend, Data no longer cared if he hurt La Forge, with matters being made worse as Lore had managed to work out a way to make Data experience emotions while only allowing him to experience negative ones. Using a Borg interlink transceiver, Captain Jean-Luc Picard and Deanna Troi were able to generate a Kedion pulse that created interference in Data's positronic net and caused it to reset his subroutines to normal; although Data was still only experiencing negative emotions, he was once again able to choose whether or not to act on them. (TNG: "Descent", "Descent, Part II")
Aboard the USS Voyager in 2375, The Doctor developed a feedback loop between his cognitive and ethical subroutines after making a subjective decision which cost the life of a crewmember, Ahni Jetal, having 'allowed' her to die when she and Ensign Harry Kim were both injured by the same alien weapon, the Doctor only able to save one of them in the time available and selecting Kim simply because he knew him better. As a result, he began to have a "mental breakdown" of sorts, berating himself and his abilities as a doctor and blaming himself for Jetal's death. (VOY: "Latent Image")
The crew of the USS Equinox disabled their EMH's ethical subroutines so that he would not object to killing Nucleogenic lifeforms to increase the Equinox's warp power. In late 2375, with their EMH 'hiding' on Voyager, the Equinox crew also disabled The Doctor's ethical subroutines, and, in his altered state, he extracted information from Seven of Nine's Borg implants. After his ethical subroutines were restored, the Doctor apologized to Seven, but she assured him she bore him no ill will, and offered to help him modify his program so that future attempts to tamper with it would be much more difficult. (VOY: "Equinox", "Equinox, Part II")