Ask HN: Ethical to I work on my own projects at work

Technically I am a software developer and that is my role at the company, but we actually literally have no software work since the focus is on our hardware implementation. So most of my day is making WordPress updates or working on the CRM. Alot of downtime. Beside legality over intellect property on my projects working on company computers (don't think my employers will ever find out), should I work on my own stuff? Preventing brain drain? Isn't that what Einstein did at the Patent office?