The Martians feed Forbin a virus to program in to the successor of Colossus to end the second book.
The third book the Martians force the Earthlings to build a machine to harvest oxygen to save the Martians but Forbin uses WW I battle ships to destroy the Martian machine while the restarted Colossus tries to stop him.
Crazy stuff.
As I recall the last two books were also a good bit misogynistic.