Experts are questioning whether North Korea was behind the WannaCry cyber attack amid suggestions it does not fit the pattern of previous hacks blamed on Pyongyang.
Some suspect a group known as Lazarus, believed to be a mixture of North Korean hackers operating in tandem with Chinese "cyber mercenaries".
Identifying hackers behind sophisticated attacks is a notoriously difficult task, and proving they are acting under the explicit orders of a nation state is even trickier.
S ome experts see the latest attack as an anomaly. Michael Madden, a visiting scholar at the Johns Hopkins School of Advanced International Studies and founder of North Korea Leadership Watch, said if North Korea was responsible, it would be an entirely new type of cyber attack by Pyongyang.