Any miner that would want to steal a block fee would have to mine <i>two</i> blocks in succession before the rest of the network gets another one.  It&#x27;s possible, but quite unlikely, and if you don&#x27;t pull it off you&#x27;ve thrown away a lot of hashing cycles.  The only way to make it probable is to control a majority of the network hashrate, but in that case, there are much larger problems afoot (i.e. a 51% attack).<p>It does place an upper bound on the total amount of BTC that can be laundered through transaction fees on a single block, though.  I won&#x27;t do the math right now but it&#x27;s some multiple of the block reward fee that depends on what percentage of the network hash rate you control.<p>Fortunately (?) for the would-be launderer, the average pool is mining a good deal more than one block per day, so you just spread your laundering across a series of blocks.