recently i've seen that Google AdWords is sharing promotional codes, which gives you $200 for publishing with them.
The question is this: Obviously, the code is a big combination of chars, something like: 9842 - a251 - b51s - 1250
, and if you try any other input but what they give it will fail telling you that the code is not valid. It's of course good because you don't want any "robot" to generate your codes for you.
So, what are the best practices for do something like this? I've been thinking and using a big amount of chars, and generating them in random sequences could it be done, but i think that some "probabilistic" model would fit better.
Do you know how is it properly done?
Thank you all!