“Earlier this month the Pentagon entered a new phase of its air campaign in Iraq against the Islamic State when it announced that AH-64 Apache helicopters would assist beleaguered Iraqi and Kurdish ground forces. Almost simultaneously on Twitter, the Islamic State released a how-to guide on how to shoot down the heavily armed aircraft with a man portable air defense system or MANPADS.”
Source: Islamic State has a guide to shoot down Apache helicopters with MANPADS – The Washington Post