I won’t tell you where I used it, they fixed it anyway. But I will tell you how I did it and you might be able to find similar bugs in some other ppc service.

It was a quite new small ppc company that offered both advertising and publishing. And like most others they had a minimum bid requirement and the quality of the traffic wasn’t very good. It was hard to make profit even at the smallest bid. But one day it came to my mind, I tried to hack their minimum bid check, I typed ”1-0.9” into the bid box, and it worked! It passed the test of a minimum bid of 1 cent and then it calculated 1-0.9 and abra kadabra! I had just got my bid of 0.1 accepted! I went lower, and lower. Down to 0.0001¢, Ye that’s $0.000001! I used it for simple PPC arbitrage as the quality of the traffic wasn’t good for anything else. But the ROI was extreme

If you have some basic programming skills you should probably be able to come up with things to write in the bid box to hack the bid. Don’t expect it to work with any big ppc company though. If it’s legal? Hell do I know.