branches of the services are very concerned about it. they're reminding soldiers, airmen and marines to be careful of their surroundings. >> reporter: the fbi is warning members of the u.s. military to be aware of and review their online social media postings as well. the goal? to make themselves less of a target to a terror group with an unrivaled and aggressive online operation. the bulletin obtained by cnn advising members of the military, quote, to use caution and practice operational security when posting. one grave concern of u.s. counterterror officials is its so-called lone wolf attacks require very little planning and little, if any, direct contact with isis commanders abroad. >> the new phenomenon that i see that i'm very concerned about is somebody who's never met another member of that terrorist organization, never trained at one of the camps, who is simply inspired by the social media,