The great fallacy of spam filtering is that access control SHOULD be probabilistic whenever it is easy to implement that. Let's look at the physical world where implementation is harder. It's very unlikely that I'll arrive home from work at 4:30 AM, AND that I'll be driving a rental car instead of my own car, AND that I'll be wearing new shoes with a sole pattern that my smart walkway hasn't seen before. So, ideally my home security system would automatically call the police. Right?