Why Attorney General Says ISIS Is More of a Threat Than al Qaeda

ABC News' Pierre Thomas speaks with Attorney General Loretta Lynch.

— -- The nation’s top law enforcement official says the threat from ISIS is so great because the terror group's technologically advanced tactics are “still new to us," and the U.S. government is “still trying to determine the scope” of efforts to radicalize Americans and others around the world.

That threat environment comes from ISIS’ unprecedented social media campaign on Twitter and elsewhere, using slick advertising and online messaging to encourage followers worldwide to launch attacks at home.

“They've got over 20,000 English-language Twitter followers,” Lynch noted.

“As people get drawn more and more into the rhetoric, they move off of [more mainstream] platforms … into encrypted platforms into which we don't have visibility,” she said, adding that federal authorities call it the “going dark” problem.

“I think that the fact that he was not on law enforcement's radar illustrates the concern that we have of individuals who are outside the mainstream yet tap into these strands of thought or schools of thought that lead them to violence,” Lynch said.

She also cited a potential new threat from ISIS and others looking to harm the United States: a cyber-based terrorist attack.

“That is the thing that keeps me and many of my colleagues in law enforcement up at night,” Lynch said.