Welcome Apple users to the real world, where your devices are constantly hacked.
No Apple devices have been hacked, Jonty. You're right about constant hacking. . . and that's what happened. . . but it was Windows machines that were hacked. Millions of IDs were stolen from hacks at Adobe and eBay including those of Apple device users and the criminals are using a safety feature of iOS and OSX to remotely lock the Apple devices through the owners' Apple iCloud account as if the Apple device owner were doing it himself.
This is another form of social engineering based on people's tendency to use the same password across multiple accounts. . . and the knowledge of their prefer to not use a pass code to access their devices. Both poor security practices used by owners of all devices. The Apple devices have not been breached. . . they are just as secure as they were.
That said, with the same access the criminals could remotely erase the data from the devices! Not access, and they also have access to the email account and any photos of the breached iCloud user. Not good. Moral of this? Don't use the same password on your iCloud account that you've used anywhere else!