Hamas

If Hamas had attacked only IDF bases and outposts by surprise, including killing/kidnapping soldiers and women (without rape and beheading), would this have been a legitimate military action? And in general, if a soldier is on guard duty in the territories/or just standing at a bus stop, is it considered a terrorist crime if an Arab from the territories/Gaza harms him, or is it legitimate, as in a regular war, since he belongs to the enemy army? (In the current situation, I'm not sure that this can be answered freely… but let's try 🙂 )
This intrigues me both from a moral and international law perspective.