(emphasis mine)
People say things like this without fully knowing what they are talking about. I had one friend that told me that SHA256 was proven to have weaknesses and that somebody very smart could crack it in minutes. Well, if that's the case, then why has no one heard about such an attack? (And I'm not talking just about Bitcoin, but about any system that uses SHA256 in one way or another).

The algorithm has been proven to be very secure, and so it would take decades (if not more) for someone to even think about a real, useful way to crack it (because you just can't brute force it even with quantum computers without wasting hundreds or thousands of years).

And if suddenly someone discovers an unknown vulnerability, it won't get unnoticed for very long, and there will be news all over the world about a system hacked in such a way.

So, no. Although your statement is technically correct, it's not going to happen any time soon.