Facebook allows its authentication credentials to be stored in plain text within the Apple iOS version of its mobile app. This effectively gives another user access to your account, profile and all on that iOS device. Facebook has responded that this issue only applies to compromised or jailbroken devices. Facebook’s native apps for the two platforms not encrypting your login credentials, meaning they can be easily swiped over a USB connection, or more likely, via malicious apps. Facebook says there’s no way to fix this problem.
Source: https://thehackernews.com/2012/04/your-facebook-credentials-at-risk-on.html