Data security and encryption schemes are designed by fallible humans, not omniscient Gods, so any scheme that can be devised can and probably will eventually be broken. The literature is rife with famous or infamous, according to your viewpoint, examples of this. So it is safe to say that with electronic data there is no such thing as absolute security. Given sufficient, time, money, and resources, or an ingenious breakthrough algorithm, any security scheme will eventually be broken. In the final analysis the best that you can hope for is to accomplish one of two things:
  1. make the resources required to break the security system so expensive that it costs more, perhaps many times more, than the value of the data to be gained or…
  2. it will take so long to break the scheme the data simply is no longer relevant.

This is particularly true if you have physical possession of the device containing the data. The weakness in Apple's scheme is, of course, the passcode. If you have the iPhone and the passcode, or you can guess the passcode, there is zero security. If you only have the data or even the data and the passcode, but you don't have the iPhone itself the difficulty is increased exponentially. Just because you know the security algorithm and you have broken into the data from one iPhone, the next iPhone is a whole new ballgame.

If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein