The BTC puzzle is to find the privkey in a certain range for an address. And I found that some people solve this problem just like mining BTC. Such as the pool ttdsales/66bit/login.php. I found that the pool probably generate a random address and you should submit something relevant to the privkey of the address as a proof of work. And the pool client is not open-source. I think maybe someone cracked the software and submit the answer once the privkey of the random address is found. So if the solution is found,the hacker may gain more reward than usual. And it may cause the pool can't find the solution.