You will see in a report. Google will not credit you (cash) but will report huge amount of them. Also, watch out for CTR rate, if its too high, that the sign!
its always been a bit of a dark thing. goog tend to see invalid clicks all over the place! who, what, where or when your ads are being invalidly clicked is a question with a question mark...
check your CTRs .. usually they should be less than 2% if you have a high traffic site.. or atleast they should be consistent .. if you find something unusual, report it to them