While the hunt still goes on for the three teenage girls from London believed to be travelling to Syria to join IS there are calls for Twitter and other social media to do more to shut down websites used to disseminate IS propaganda and aid recruitment. One of the missing girls was reportedly following more than 70 Twitter accounts belonging to terrorist fighters or IS sympathisers; one of those is a British woman who tweets about life as a jihadi bride. IS has deployed social media in the battle for ideas as effectively as it has boots on the ground and there's a terrible, but inescapable irony that they're using one of the values that we hold most dear - freedom of expression -against us. Twitter says that it has a policy of not monitoring user content, but takes action when alerted to inappropriate posts by other users. Many social media sites see themselves as platforms rather than publications, and argue that it's not their job to police people's views. But is that a morally sustainable argument when vulnerable young people are being groomed online? Is it morally inconsistent to defend the rights of publications like Charlie Hebdo, but at the same time demand that the views of those who support IS are supressed? How far should we be willing to sacrifice freedom of speech and our privacy in the fight against terrorists on the internet?