content: Only a matter of time until a fingerprint database is hacked and distributed.  Same with "voice prints". When technology catches up (5 years? 10?) and people can 3D print finger or live-modify voices, this will be hot stuff for hackers. Like Iwasherefirst says, stick with things only you know in your brain which can be changed if necessary - never use things that you are which can't be changed (limited supply of fingers and your voice).