Ah yes I trust facebook so much I'm going to give them my fingerprint.,(reply>), Biometric authentication data is only stored on your phone and that data is put through an irreversible mathematical process that changes the numbers around, called a hash function. Only this string of numbers in the hash function is sent to facebook that is stored on their servers. Of course on the way to facebooks servers through the internet the numbers are encrypted, meaning the numbers are changed in a way only facebook is able to reverse, so other people can't see your hash string. The hash string serves as your password basically. Actual passwords are also put through a hash function to prevent anyone else to see what your actual password is.,(reply>), Just because you're authenticating  with touchid on whatsapp, doesn't mean Facebook has your fingerprint.,(reply>), Hell, with a halfway decent phone you can hand over your irises, too, just in case.<br><b>It's possible that you already have!</b>