experts say north korea may be behind the ransomware that infected hundreds of thousands of computers worldwide. why is it being said that north korea could be behind the massive cyber attack? >> reporter: these really are the top lines in the world. if you look on the screen you see code from wannacry, the malware in this latest attack and also code from the lazarus group which was tied to the sony pictures hack in 2014 which the u.s. has blamed on north korea and actually charged north korea for that attack. you look at the two boxes, and you can see sections of code that are exactly the shame. that's what the researchers are looking at. it's not definitive. early days, could be a false flag by the hacking group to make it look like north korea but this is what they are thinking and there are similarities by other hacking attacks by north korea. a major attack. 300,000 machines affected in 150 different countries. critical infrastructure, hospitals shut down as a result of this so real lives at stake and they can do this attack