US officials are worried by the capabilities of the ISIS members for keeping their communications covert. US Defense Secretary Chuck Hagel admitted that ISIS is dodging the US Intelligence. ISIS members have proven exceptionally difficult to track due a proper use of technology tools, like encryption, social media platforms and encrypted instant messaging platforms. ISIS is also using a commercially available service that allow to permanently delete messages sent via the Internet, like the popular application FireChat that allows users to send messages to each other without connecting to the Internet.”]
Source: http://securityaffairs.co/wordpress/30271/intelligence/isis-avoiding-us-surveillance.html