From other answers in the comments, it's fairly clear that the vast bulk of these are some sort of botnet which are paying out their SP in power down (since that's what this particular transaction represents) to another account. To really find out how they were earning it, I would have to point some more code into specifically pulling their transactions, but I'm pretty sure that these are all some kind of vote botnet.

There are a rare few which are legitimately someone's multi-account, but the rest…

Good times, good times.