A computer program was a set of instructions for a computer. A person who wrote programs, such as Melanie Bush, was known as a programmer. (TV: Terror of the Vervoids, et al.)
The Seventh Doctor claimed that all the best computer programs, such as the one the TARDIS used, were written in ancient High Gallifreyan. (PROSE: Timewyrm: Genesys)
Known computer programs included one created by a sentient crystal ball in 1925 to trap the Twelfth Doctor, Clara Oswald and Harry Houdini; (COMIC: Theatre of the Mind) Voractyll, created by the Voracians to take over the computer systems of Earth in 1998; (PROSE: System Shock) and Mann, created by Jess Carter in the 27th century to help her learn social interaction; (PROSE: Welcome to the Machine)