american military on u.s. soil. the first time an fbi bulletin has included such a warning and cites attacks s is in canada. >> all commanders are concerned about it, reminding them on a daily basis to be careful of their familiar surroundings. >> reporter: they're reminding the military to be aware of and review their online social media postings, as well. goal, to make themselves less of a target to a terror group with an unrivaled and aggressive information. bulletin obtained by cnn advising them "to use caution and practice operational security when posting." one grave concern of u.s. counter terror officials so-called lone wolf attacks require very little planning and little, if any, direct contact with isis commanders abroad. >> the new phenomenon i see that