I just want to know how those people behind bitcoin secure the money they will invest because as far as I know there are lots of hackers all over the world.
No doubt that investments in any cryptocurrency including Bitcoin are very risky. Your wallet can be hacked (for example by social engineering) any time.
Of course, every trade, or person related to cryptocurrencies should recognize that there are a big fluctuations, manipulations and risks to lose money. That's why every experienced trader rate according to principals of diversification and risk management. That's why you should even save your assets in several wallets and don't use simultaneously.