The officials wouldn't go into details on how they know this, whether it's terrorists switching email accounts or cellphone providers or adopting new encryption techniques, but a lawmaker briefed on the matter said al-Qaida's Yemeni offshoot, al-Qaida in the Arabian Peninsula, has been among the first to alter how it reaches out to its operatives.
The lawmaker spoke anonymously because he would not discuss the confidential briefing by name.
Shortly after Edward Snowden leaked documents about the secret NSA surveillance programs, chat rooms and websites used by like-minded extremists and would-be recruits advised users how to avoid NSA detection, from telling them not to use their real phone numbers to recommending specific online software programs to keep spies from tracking their computers' physical locations.
House Intelligence Committee Chairman Mike Rogers said there are "changes we can already see being made by the folks who wish to do us harm, and our allies harm."
