Some time ago the breakdown was dangerously close to heaving too heavily towards Deepbit with only a small part unknown/single person miners. Now there's a 34% unknown factor.
What caused this? Are these botnets? People deciding their amortised profit stablises anyway? A drug cartel laundering money?
It is unlikely that we will account for most of the activity, as Bitcoin allows for high anonymity. Some of that hashing power is believed to come from some botnet, but one can't be sure. You could try looking for the owners of the IPs that relay the new blocks and check who they are, but that would be a tedious work that could be easily hidden, for example by relaying blocks through TOR.
