by any means necessary, for their children to be safe. >> reporter: ted rowlands, abc news, los angeles. disturbing information about americans fighting for isis. intelligence agencies believe as many as 150 americans have tried or succeeded in reaching the war zone. some died there and a small number are fighting with extremists. they are part of a wave of foreign fighters streaming in to iraq and syria to join isis. here at home, a stark terror warning is set to be issued today by top u.s. intelligence officials. since last month, isis posted 250 on-line publications, much of them on social media urging radicals to attack in their home countries including here in the u.s. no specific plot has been identified but a new government estimate says there are a few hundred potentially violent extremists here on u.s. soil. that warning comes on the heels of another hack attack targeting a major american news organization. hackers managed to commandeer the twitter account for "newsweek" magazine sending dire threats.