How secure are Dropbox, iCloud, Google Drive and OneDrive?

If you were to be influenced purely by the more tabloid of tech publications, with headlines screaming about hacked databases, compromised passwords and secret service data probing then you wouldn't touch the cloud with a bargepole. How secure are Dropbox, iCloud, Google Drive and OneDrive. Truth be told, cloud services are not as insecure as the headlines make out. Indeed, there's much to be said for the argument that Dropbox, iCloud, Google Drive and OneDrive have both the money and motivation to make their data stores much more secure than you could hope to achieve on your meagre budget yourself. So let's take a look at these four services...