There's no way they actually earned $500M/year. Even if Whatsapp had 100 employees making $200k/year on average, that's $20M on salaries. Add an another very generous $80M on infra/admin etc costs and they'd have been making $400M profit. With that much profit achieved within such a short period, in the QE funny money era they could have IPO'd at $50-100 billion easily.