Re: @palpy: Yup. Quite bullshitty.
"But the greater question remains: What if trawling through online files, whether OneDrive or Dropbox or some nasty repository on the darkweb, gets some seriously psychopathic predators put away? "
And what about when they get it wrong? When they report someone's innocent files as child porn because the person at microsoft doesn't get the context of the file? Maybe I decide I don't like you and add some things to an account in your name? And what else are they looking for using automated systems? Perhaps you are stupid enough to share some code snippets with some friends on there? Perhaps some other data that someone at microsoft decides is more valuable to them than to you? Why are they going through your files when other cloud storage companies don't and even make it so that they can't, only the owner and those they share it with?
I run an Owncloud server for me and some friends. The server copies of the files are encrypted and I cannot see what is in there. that seems to be the default for everyone else other than microsoft. Why are they doing this?