I submitted probably hundreds of clicks in the past couple of months from networks owned by or run by the same company that were clicking on our Google ads apparently. When I tallied up the number of clicks based on analytics from our logs and compared it to the clicks in Google - I can see that a number of clicks from these networks were included in the clicks we were charged for by Google. We have very detailed logging in two forms in a way I can easily query a database to get a very accurate count.
I contacted the network from whence the nasty clicks were coming and they claimed they were not doing it. They claimed they never hit our sites. The clicks stopped as soon as I contacted them and they blocked out traffic from their networks at the firewall level, so clearly those clicks were the result of some kind of hack or maliciousness because they wouldn't block it out if it was valid.
Google responded by telling me not to worry - that they never charge for fraudulent clicks. I hope they mean that they are going to review my traffic and clicks and give me a credit...