It began as a plan for a very normal 16 birthday party.Merthe Weusthuis wanted a quiet celebration with a small group of frind in her family home in the small Dutch town of Haren. Like many teenagers, she decided to send out invitation via a social network site. But Merthe made one big mistake: she used open-access settings on Facebook, so it wasn't just her frinds who could see details of the event, lots of strangers could too.