SHA256 has been the world standard for secure hashes for quite a long time. its the backbone almost all secure internet encryption systems such as TLS, SSL, PGP, SSH, IPsec, and S/MIME

About 3 years ago, a research group announced they had found a way to produce a SHA256 collision under controlled circumstances this is another way of saying the algorithm has been 'cracked'. Within a day they backtracked and said it was an incorrect conclusion from using faulty equipment. You'll have to believe what you want to believe in this case.

Here are a couple pages to start learning more about how SHA256 works