Several years ago one of my bikes was stolen from off the strap-on rack on the back of my car. They lifted both bike and rack off the car, destroying the trunk lid and the rack, tossed the bike in a truck bed, and off they went, all in say 15 seconds. I unfortunately know all this because I heard the commotion and ran out in time to see the b**tards peeling out of the parking lot. I switched to a locking rack after that.

Definitely find a way of locking the bike and rack to the car.

Kim