Obtained, read, viewed, learned, discovered.

The knowledge wasn't obtained illegally or illicitly, immorally perhaps.

Illegal entry/trespass is a crime regardless of the method used however.

In your analogy copying the code (online content) isn't necessarily illegal, however using that knowledge without compensation, permission or attribution may be a crime (depending on copyright law, judges rulings etc).

This point makes sense to me. I agree with "learned" and "discovered".