Not common in my neighborhood.I was going to buy a vacant house. It was burned down by a homeless person using a charcoal grill for heat. You'd be surprised how often it happens. A house was foreclosed in my neighborhood a few years ago and a homeless person broke in during the winter. It's incredibly common.
The house and barns next door were vacant for over a year. We had live fire room clearing drills. Never had any squatters hang around.