If you've ever been stung by someone sharing something online about you that you'd rather they hadn't, you've experienced the difficulties of maintaining privacy across social networks. In this video, Professor Derek McAuley explains just why it's so complex.

He starts with a very good point. Human social dynamics have evolved over ten of thousands of years into a very nuanced system of behavior; social networks came along and changed everything in the space of years. So, it's no surprise we've struggled to adapt. Watch the rest to find out why, really, we're not doing too bad a job—and how we can do better. [YouTube]