How to generate 63 million prize codes
<p>I am trying to come up with a "smart" and "secure" way of generating about 63million unique codes to be used in a competition. The codes will be about 10 characters long.</p>

<p>Has anyone done anything similar or aware of any "hurdles" that might arise from this issues? How do we minimize the probability of someone being able to guess the codes?</p>

<p>This project will be done in PHP, but that won't really matter, it's more of the logic that's an issue here.</p>

<p>Any feedback would be really appreciated.</p>

<p><strong>UPDATE</strong>
Just to clarify it will be 10 <strong>characters</strong> of case insensitive Alpha Numeric Values.
A-Z0-9 </p>
