intelligence? >> it is extremely difficult, virtually impossible. first we don't have an embassy in pyongyang so that limits the official diplomats or any kind of agents we might run. also just trying to blend in. obviously we stand out because of different ethnicity. also even south koreans try and run operatives, they have difficulty. different dialects, different use of words, pronunciation, the populist is suspicious of any foreigner, anyone they don't recognize. >> reporter: north koreans who talk to foreigners without permission could wind up thrown in prison camps or even executed. there are not a lot of phone or internet signals to hack. this photo from space shows what a dark country it is. and while spy satellites can look for activity at launch pads and nuclear sites, u.s. military officials say north korea has stepped up its efforts to hide many of its weapons activities. >> they have learned from watching how we attack targets how to bury things deep underground complexes.