My guess is that someone has written a nice new virus for GPU mining and wrapped it into several games or other programs available as torrents. You can imagine if you seed a copy of a new game that's popular and 20,000 gamers download it, achieving such a hash rate is quite easy.
1,920,385 kh/s is equal to x3200 HD7950 working on 100%, but such load makes it hard to even use PC. And not every PC has such expensive VGA.
So if it is a virus, it has tens of thousands PC infected. Botnets with this amount of bots are VERY risky, hard and expensive to use 24/7.
Maybe just admin uses fake stats, to grab LTC from pool (or another exploit).