How secure is the passcode?

Hi,

My iPhone was stolen this morning. I set the passcode on it, and I also enabled the option 'Erase data after ten failed passcode attempts'.

The question I wanted to ask is how secure is this? Can this feature be overcome in any way? Can whoever took it get to the data I had stored on my phone?

Any answer will be much appreciated.

 

No, it was a random one that I made up.

Thanks, that makes me feel a teeny bit better.