What was once permissible, is now forbidden. What was first allowed, is now punishable. What was initially tolerated, is now a crime against the State. This is what happens when the conception of what is illegal is confused with what is actually evil.
Mala in se is the idea that something is wrong or otherwise evil in and of itself. These are actions that are so abhorrent that they can never be reconciled with human liberty. Such conduct includes theft, kidnapping, murder, and rape. The understanding of these behaviors were developed into Common Law offenses.
Mala prohibita is the legal notion that something is illegal only as a violation of some sort of statute, instead of being inherently immoral. While not necessarily wrong or even despicable, illegal conduct is as such because a code or rule of some kind (such as statute that is passed by a legislature and enforced by the police and various bureaucracies) has been technically broken. This can range everything from truancy & practicing without a license to tax evasion & copyright infringement. It is quite typical for most, if not all, mala prohibita to be exclusively offenses against the State, especially if they are considered victimless.
Gauging what actions are mala prohibita without being mala in se is a tricky, yet integral, proposition. Defending yourself from the initiation of violence by someone else is in accordance with the Non-Aggression Principle, but what if that initiation of violence was being done by a bureaucrat, a legislator, a judge, or (dare I say it?) … a police officer? Granted, physically defending yourself from any of these agents of the State is mala prohibita, but the question is, would it be mala in se? Or how about sabotaging government property? Instead of a SWAT team killing more innocent people (just like the militarized police have done with Vicki Weaver and Jose Guerena), what if by removing the firing pins in their guns you saved their lives? Would that really violate mala in se?
Just food for thought. As always, only you are ultimately responsible for what you decide to do. Your life is your own. Make it count.