Assuming that you are talking backpacking in the boonies type hiking, I don't think that solo is all that great an idea, just 'cuz it is sooo easy to hurt yourself to the point that you need help. No partner, help might be a long time coming. As far as bad guys go, it is my experience that they are lazy SOB's. They might break into your car while it is parked at the trailhead, or try to jump you near the parking lot, but they ain't gonna hump ten or so miles back into the boonies to work their trade...