explosives. that bulletin reportedly says the minor had obtained explosives instructions and was spreading them through social media. in new york, officials already gearing up for an unprecedented security test. the large screens at many police headquarters showing many high priority concerns during an exercise by homeland security. >> this event is going to be the largest security challenge that the department and the city have ever faced. >> reporter: the papal visit coincides with the 70th anniversary of the united nations which will bring 170 of the world's leaders to the city at the same time. >> we can say safely we have literally never seen something like this before and we welcome it. we embrace it. we look forward to it. >> reporter: this latest arrest illustrates how isis social media is reaching young people, even inspiring them to attack the pope while he's in the u.s. as with the vatican, new york authorities say that they know of no credible threat against the pope.