"If someone hacks your password, you can change it - as many times as you want," Franken, a Democrat from Minnesota, said in a letter sent Thursday to Apple CEO Tim Cook. "You can't change your fingerprints. You have only ten of them. And you leave them on everything you touch; they are definitely not a secret."
Franken added that a fingerprint uniquely identifies its owner, unlike a string of numbers and letters.
"Let me put it this way: if hackers get a hold of your thumbprint, they could use it to identify and impersonate you for the rest of your life," he wrote. Franken's office released the letter to the media Friday.