Mat Honan (the writer caught) tells the full story here

At the end he identifies the faults in the system (including his own). On my reading, there are two main reasons why this hack was possible. The first is acceptance of the benefits of having all your devices and data connected 'in the cloud', without taking extreme security and local backup precautions. If you do this, you put all your devices and data in someone else's hands.

The second reason is the ridiculous use by Apple of the last 4 digits of a credit card number as a security check. This is the only bit of credit card information that is universally available. They are printed on almost all card receipts.

Phil