How many warnings does Google give before Banning Adsense?

I have heard from one of my friends that Big G is sometimes graceful in granting you a couple or may be even more warnings before eventually banning you out...!!!!

Anyone go a clearer picture?? Has this occurred to anyone here?

 

Anywhere between 0 and some undefined integer greater than zero (inclusive).

 

some people are fortunate to get 'a' warning, then literally 5 seconds later their banned.

 

I think it will depend on the user problem. If you use any autosurf program or something like that some times it will send warning message if again you are continuing that work means second time it will ban. Some times for invalid clicks without getting warning from them it will ban instantly