My name is Dennis Delaney. I wrote a novelet for Creative Computing magazine in 1979 entitled "The Contradiction Theory" that was published in their book Tales of the Marvelous Machine. It was a murder mystery/sf tale dealing with the then unknown concept of a Trojan Horse virus. Is this it?
Detective Tobias Warton tries to solve the murder of Philip Carmichael, a man who's been trying to unite Mechanists and Anti-Mechanists, during his secret visit World Computer and Robot. His method of death is simple to determine. The air in his room was removed via a computer command. Detective Warton has to determine whether this was a matter of mere error, or if it is something more malicious.
Partway through the story, a programmer, Raudive Allen, claims to have entered the fatal program into the system as a Trojan Horse, triggered by a dial code to Nahum Sprague, but also claims that the program was slid under his door, and he didn't know who gave it to him or that it was going to be used to target Carmichael.
Ultimately, it is revealed that it was the Governor who engineered the fatal incident in order to foment chaos.