Hacking is a vital tool to fight extremist propaganda, US State Secretary Hillary Clinton has revealed. Washington has replaced Al Qaeda material on Yemeni tribal websites with information on damage the terror group has done to Yemeni civilians.

­Speaking at a conference of US and international special commanders, Clinton said cyber intelligence experts were able to take down pages extolling the murder of Americans and substitute them with pages describing the toll al-Qaeda attacks have taken on Yemenis. She noted that the extremists responded by telling supporters not to believe everything they see on the Internet.