I've been looking at blockchain.info for a while and I already saw it happening twice that a block was confirmed with only a single transaction inside. The first time I saw this, I found it very odd that someone was so lucky to find a block so soon that there weren't any transactions done in the meantime. But now I saw it happening again and I clicked on the block for some more information.
It was block #294422 and it still seems odd to me. In fact there were no transactions done in the block but only 25 BTC credited to the miner (I guess) which has address 1K7znxRfkS8R1hcmyMvHDum1hAQreS4VQ4. Looking into this address, the blockchain tells me that this address might not be trustworthy as it has double spends. When I look into the transactions I see that this address quite often receives 25 BTC, apparently for finding new blocks.
Is this a coincidence? Did someone create a client that can actually take part and at the same time not take part to the network by finding blocks without any transactions and thus creating coins for themselves?!
Could someone explain this?
Happens all the time. No big deal. There is nothing in the protocol that requires miners to include transactions in their blocks. Of course the miner misses out on all the transaction fees if they do that, leaving all those fees from miners that mine the next block.
Could this be a bug or exploit?
Nope. Just a normal part of the design of bitcoin.
Edit: something else; block 294421 was found 47 minutes ago, 294422 was found 22 minutes ago, 294423 found 27 minutes ago and 294424 26 minutes ago. Why is this 1 transaction block 'younger' than the 2 blocks that have a higher ID?
Timestamps are not exact on bitcoin blocks. They are allowed to drift by up to 2 hours in either direction.