Ricky uses his Dad's Coco to run a code cracking algorithm and break into a military computer.
The only concern here is whether the compute power of the Coco is sufficient to break the code.
Year of feature (shown above)
The TRS-80 used a Motorola 6809E a 1-2 MHz processor with a 8/16 bit bus and a direct page register. It is not any less believable to be used for the purposes of hacking than any other home computer of the time. It was effectively more efficient than the z80 and equivalent to the 6502 used by Apple and Atari. What's unbelievable is that he wasn't thrown in federal prison for 20 years.
To be fair, anti-hacking laws didn't go on the books until 1986.