I wonder how they verify posting activity. If it's not some kind of honour system where posters report to a team leader who reports to a supervisor who reports to a etc and so on, then what are they doing?
Incidentally, it's not entirely as if this doesn't happen outside China. There's some schools of thought saying major copyright holders spend some amount of their budgets on work-at-home people who post anonymously on, say, torrent sites, downgrading the supposed quality of a given movie torrent, or talking up scare stories, to turn casual downloaders away.
This "army" does seem to have some different quality to it, though.