they note that evidence suggests the source was North Korea, but also note what I noted in an earlier post:
it hit China (and Russia) the hardest because lots of folks there use illegal Microsoft Windows programs.
It did not make any sense for North Korea to unleash Wannacry because most of the victims were in the few countries (China and Russia) that still supported North Korea. These two countries were hard hit because both depend heavily on illegal copies of Windows and other software. Most users of the illegal Windows software don’t bother to pay for security and other software updates provided by other hackers who supply these updates for a fee. Microsoft will not upgrade illegal copies of its software. Worse, even though Microsoft regularly releases free updates via the Internet many users do not immediately apply those updates (because updates sometimes break something else).
you also can listen to the podcast here.