There was an hourly contractor I knew that used company A's laptop and wifi connection to do work for Company B, doing code check ins on Company B's open source github with his real name.

He would go hide into some office in Company A for a couple hours during the work day doing some kind of meeting, hoping that no one would notice him behind the glass walls.

Meanwhile his performance sucked for Company A, and he couldn't handle apparently simple tasks either. The github check-ins were flagged by the firewall, and they summarily let him go as soon as they saw it.

I would not hire him if his resume crossed my path again.