The Daily Beast reports that the US military (read: NSA) is having a hard time tracking ISIS members because ISIS is doing a good job maintaining operational security. These fighters are working hard to evade NSA spying, using encryption and commercially available software that lets them email each other on local networks, avoiding the NSA-tapped global internet.
People who are doing big illegal things often go to extreme lengths to ensure they aren't electronically monitored. Osama bin Laden, for example, never touched the phone or the internet. He knew full well—before Edward Snowden's leaks—that the US government was monitoring global communications. So he used couriers to communicate, not the internet or cell phones. Meanwhile, hundreds of millions of totally ordinary people are subjected to invasive government monitoring and surveillance. Why? Because they don't go out of their way to avoid it. They "have nothing to hide," after all.
I call this the 'security paradox'. It's why dragnet surveillance isn't just bad for democracy and liberty, but also terrible security policy. Dragnet surveillance doesn't catch advanced terrorists or criminals. It just catches the rest of us.