Gaming datanet hacking in Highwayman should be enacted as it is with the Dark Future Datanet rules. The only difference should be with the skill rolls.
All skill rolls are opposed, and all rolls should be made using the Computer skill + 5 per rating of relevant program being used.
If the hacker doesn't have the Computer skill then their skill roll is made untrained. The same applies to any nodes that don't have running software (such as an empty security node) and viruses.
The losing side takes damage. The type of damage depends on the target.
Plug: The user of a plug takes 1d6 damage, which is applied directly to the characters hit points. Armour and other forms of defence do not apply and cannot block this damage. Even if the character falls unconscious, they will continue to take damage until they are dead or have jacked out.
Virus: A virus that loses an attack takes 1d4 points of damage. This damage is applied against the programs that the virus has, each point of damage degrading a program by 1 rating. Armour programs are lost first, then the program that is being used to attack, finally any other program takes the rest of the damage.
Operator: The operator and their computer take no damage, but their programs take damage as if they were a virus. Once all programs have been destroyed, the operators computer may be traced and then attacked normally.