​According to The Hacker News, a team of security researchers has discovered a critical implementation flaw in major mobile banking applications that could leave banking credentials of millions of users vulnerable to hackers.  Basically the flaw leaves users open to a Man In The Middle Attack and as such user's PIN numbers as well as other account information becomes possibly susceptible to these attacks.

https://thehackernews.com/2017/12/mitm-ssl-pinning-hostname.html