An unknown major solo miner (currently IP 220.127.116.11), most likely a botnet, is relaying blocks with zero transactions. Two weeks ago this miner constituted ~15% of the network, now it constitutes ~30%. If the growth rate continues, in about two weeks this miner (most likely a botnet) will control more than half of the network, theoretically allowing a 51% attack. It has already orphaned two perfectly valid blocks. (Thread on BitcoinTalk)
It seems to me we have an imminent threat to Bitcoin itself. Requiring transactions to be included in a block won't work; the miner can just send coins to itself. Blacklisting IPs in the client won't work; the miner can easily switch IPs. How can we stop this?