I have two Windows 10 machines sitting side by side both sucking off the same sub router, which in turn is connected to the park's free wi-fi (Working on the secure side, but the installer screwed that up).
I have had several cases where my backup Anti-Virals has found mostly PUPs that appeared only one one machine and one genuine infection that the Anti-Viral and I worked together to kill off that also appeared on only one machine.
So I do not think Malware crosses via Microsoft accounts.
Suggestion all Windows 10 folks.. Go to the STORE and type in US Constitution, Download, Read.. You can also get the Declaration of Independence. Good reading, nto as long as most folks think.