"This (ISIS) is a different kind of challenge than the sort that we had with an organisation like Al Qaida, that involved highly trained operatives who were working as cells or as a network," Obama told reporters at his year ender news conference.
"Here, essentially, you have ISIL trying to encourage or induce somebody who may be prey to this kind of propaganda, and it becomes more difficult to see. It does mean that they are less likely to be able to carry out large, complex attacks, but as we saw in San Bernardino, obviously, you can still do enormous damage,"Obama said.
This is because despite the incredible vigilance of all of law enforcement, homeland security, et cetera, it's not that different from them trying to detect the next mass shooter.
Seeking balance between privacy and intruding into communications of terrorists, Obama observed the issue of reviewing social media for those who are obtaining visas, may have gotten garbled a little bit.
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"And our law enforcement and intelligence professionals are constantly monitoring public posts, and that is part of the visa review process, that people are investigating what individuals have said publicly, and questioned about any statements that they maybe made," he said.
"But a private communication between two individuals, that's harder to discern, by definition. And one of the things we'll be doing is engaging with the high-tech community to find out how we can, in an appropriate way, do a better job, if we have a lead, to be able to track a suspected terrorist," Obama said.