FBI: ISIS Bigger Threat to US than Al Qaeda

The Islamic State terrorist group is a bigger threat to American security than al Qaeda, according to the head of the FBI.

In an address to the Aspen Security Forum, FBI Director James Comey said ISIS's effort to inspire troubled Americans to kill at home has become more of a terror threat.

The FBI has made a number of arrests in the last eight weeks. The suspects were people who had been radicalized. There are still hundreds of investigations pending.

"If you imagine a nationwide haystack, we are trying to find needles in that haystack," Comey told CNN.

"And a lot of those needles are invisible to us, either because they are communicated or just because they have communicated in a place that we can't see them," he explained. "And knowing there are needles out there that you can't see is very worrisome."

ISIS, Comey warned, is "not your parents' al Qaeda."

"It's a very different model," he said. "And by virtue of that model, it's currently the threat we are worried about in the homeland most of all."

Comey also noted the group has seen success in recent months after a year-long social media push to radicalize young Americans and Europeans.