See: https://arstechnica.com/security/2017/05/an-nsa-derived-rans...
See: https://arstechnica.com/security/2017/05/an-nsa-derived-rans...
Once it's infected a host, the SMB scanning for vulnerable hosts is launched and secondary infections begin with no further user action required.
So far it seems an hypothesis and nobody has shown such an email attachment, which is strange considering all the systems out there which save and archive attachments. Especially hospitals and gov't sites saves it all.
http://researchcenter.paloaltonetworks.com/2017/05/palo-alto...
It continues to be a very common attack method and I'd be surprised if it wasn't leveraged again.
If so, you wouldn't need a very high phish:total infected hosts ratio to explain the numbers. And given that whoever was originally phished didn't know it was an illegitimate email... not betting we'll see many examples of the initial vector.