Six years ago, stranger danger was at its hysterical height. Each night the television news showed more mothers taking to the streets brandishing placards and shouting through loudhailers, "Beast out! Beast out!", hounding those suspected of committing child abuse from their neighbourhoods.

Today these bogeymen have all but vanished. Of course there are child abusers, and child abuse is an under-reported crime, but school gates and our own pavements are no longer seen as such menacing places. But a new bogeyman has arrived. He doesn't prowl our streets, lurking instead in the ether - on the internet.