I'm trying to find the name of a novel I read in maybe 1975 where an evil hacker was taking control of a city's computers. I think he was doing this to extort money from the city.
The part I remember most clearly is that the hacker demonstrated that he could change the timing of the city's traffic lights. Unfortunately, joy-riders were counting on the timing of the lights when racing down a street. They crashed into a truck and died when the light changed unexpectedly.
Another part was the hacker was about to trip the fire suppression system in the computer center. This would fill the computer room with carbon dioxide and suffocate the operators inside. The operators had a race against time to get out before the system went off. I think the hacker could also lock the doors.
Edit: If I remember correctly, an early sign of the hacking was when people started getting water bills for absurdly high amounts.
I think the novel was science fiction in the sense of how things could be controlled by computers a few years in the future, not speculative. (But it's possible that it wasn't intended as science fiction, in which case I apologize for asking here :-)
I read Crichton's "The Terminal Man" around the same time, so I could be mixing up parts of that book.