intelligence about specific or credible plots but there has been an uptick of chatter from isis, encouraging followers to attack. the dominant concern, homegrown violent extremists, supporters of isis within the u.s. who may be inspired to carry out their call to action. >> in the year of social media and phenomenon like isil, unlike al qaeda in the old days there doesn't have to be, won't necessarily be a commanding and control relationship between somebody who instigates an incident and isil as an organization. there are self-radicalized, self-organized people on social media. >> reporter: so-called lone wolf attacks are a challenge for the intelligence community, much harder to pick up ahead of time. it's not just in washington. police forces across the nation including new york, philadelphia, and los angeles, are on high alert, and not just in the streets but online. >> there are people assigned