Just one more thought:
I agree that the likelihood to any of the blocks (and thus transactions/coins) being valid is very low.
But the most likely ones to be valid are the
earliest blocks mined. It is at least possible that your brother mined some valid blocks but then his network got isolated and the rest are orphans (stale blocks, i.e. those you won't see if you connect to the current network). If you checked mainly transactions/blocks that were mined later (and are not shown as valid), then it is still
possible (with let's say <0,1% probability) that you're more lucky with earlier ones.
If the old client shows all transactions as "valid" and "mined" (like it seems to be the case according to the screenshots) then even if there are blocks which were "really" confirmed in the canonical Bitcoin blockchain, once there is one which was not and got "orphaned", it's (almost) impossible that a further block in the chain from this moment on was accepted, because all blocks contain a hash from the block before, so no block can be "exchanged".
So I would start the process of checking the blocks/transactions strictly chronologically, from first to last. Do it like
Cricktor described here.
Good thought.
Also, was there more then one PC that he might have been using at the time. If one fell off the network but saw a block from the other that it accepted it would be very easy at that point to just keep mining forked blocks.
It's unfortunate that the transactions seem legitimately came from early days mining based from the timestamps' gaps.
But one Bitcoin client (node) can't just command all of the client to replace their blockchain with his own version of the blockchain.
I ask a stupid question..... if I put together 130 virtual machines (not a problem for me) , send coinbase transactions created with these private keys and have them authorized by the 130 machines, do you think it is feasible?
That will essentially create your own fork of Bitcoin (
an Altcoin of your creation) since you'll build your own network of nodes that will not be able to connect to Bitcoin nodes. (
since those will reject your blocks)
Its blockchain will build over from the last block that your brother mined, it wont affect the Bitcoin Network.
Or, as I have described it think of your checkbook. No matter what numbers you put it (mining locally on a fork) it does not matter. All that matters is what your bank has a record of (the real public blockchain).
That or the OP bought a fake wallet.dat that someone told him was real and we have all been wasting our time.
-Dave