Newb question

[flanger]

Hi,

I was wondering how pools deal with the fact that a mining programme could be written to just not report a successful hash. i.e. if the pool has allocated you a few billion hashes to calculate and one of them is successful (i.e. 25 bitcoins) why would the programme report it to the pool and not just claim the 25 coins??
I think i'm not really understanding how the hashes to calculate are distributed or maybe the claiming process, but I had a bit of a look around on the interwebs and couldn't see the answer...
Thanks for any enlightenment!

[deepceleron]

You cannot claim a block for yourself if you are hashing the data supplied by the pool. Part of the data that you are hashing includes the coinbase transaction address that pays the reward to the pool. If you find a block hash, it cannot be altered to pay to someone else. The pool knows what data it sent to you and what a valid reply would be, if you are hashing blocks that can pay the reward to you and which a pool won't accept, you are solo mining.

There is a withholding attack on a pool, where a miner could submit all hashes they find, except the one that solves a full difficulty block. If many miners did this, it would cause the pool to have less block finds than expected for their hash rate, and if the pool was using pay-per-share reward distribution, they could end up losing money.