1) It IS an ex BTC miner.
2) Probably not, CPUs are extremely terrible at mining LTC
3) It is, cos he's finding blocks
4) FPGAs are hardly faster than GPUs, even in BTC land. THey cost just as much if not more, but they take less power to run. It's their only advantage.
About this, it's possible:
Only needs 5 mh/s per infected PC : 400,000 infected pc * 5 mh/s = 2 000,000 mh/s, and is very secure than more than 100 000 pcs can give more than 5 mh/s
One problem with your logic: There's no way in hell you're going to get 5 MH/s per PC. Even if they're an insanely hardcore gamer, with 4 7970s (or two 7990s) in crossfire, AND he's stupid enough to not notice your malware maxing out his GPUs (a long shot), you'd only get 3MH/s. That kind of person is literally probably one in ten million. Realistically, you'll be lucky to get more than 30kh/s out of each bot, and I am being generous. So, let's see how many bots it'd REALLY take: 1,920,385 / 30 = 64,013 bots. Which is definitely doable, there are botnets in the hundreds of thousands and probably millions of systems. Looking back at your math, I don't even see what you're talking about. The guy is mining with 2M kh/s, not 2M MH/s...
ok, my bad,sorry. i change the kh/s per mh/s