[nicolaslem]

They don't use cloud providers, they use botnets of compromised computers/IoT devices.

[KoftaBob]

What's the most common malware those computers are infected with, and most common way they got infected to begin with?

[miketery]

IoT devices get infected because they usually use common software stacks that go un patched. There's crawlers always doing their thing and looking to pop these.

[JackGreyhat]

My educated guess: The most common way to get infected is via email.