Quantum Computers - what would be the impact to humanity?

Quantum Computers are an entire new breed of super-machines with multiple times more computing power than the super computers we have today. They say we'd probably see it in a decade or so, but many believe a fully functioning quantum computer is already in existence, just hidden from the public at this time. Not the test units which do exist but still incapable of major tasks, but the real deal.

Given such a powerful machine, most of the computers which keep our data, assets, transactions safe will be vulnerable. Government and military sectors would be easily breached. Business sectors would be easily hacked at will by those who have these monstrous machines; that is if they still have the old systems. On the other hand, we would see major breakthroughs in medicine happening daily. Mathematical equations and problems solved easily. We will be able to make case studies or simulations of machines, flights, space travel, agriculture, the human body and more. Its use would seem endless.

A lot of companies now are preparing and some claim that they are already "future proof" and "quantum ready", which is highly doubtful. How can someone be prepared for something we have yet to witness or know of. Most blockchain platforms now used for cryptocurrency exchanges and other functions are very secure, but no one knows yet as to what extent a quantum computer attack could be.

I feel both excitement and fear as to what the future has in store for us with these new breed of machines.