Wouldn't a combination of thumb, iris, password and voice be a pretty hard to crack method?

yup. Add a DNA profile and it gets even better.

The biometric factors themselves can't be counterfeited. But as soon as you can digitize them and transfer them over the Internet, copies could be made and fraudulently presented as the real thing, or data from other people could be substituted.

Biometrics are a great improvement over passwords, ID numbers, tattoos, microchips, and anything else man made. Those other things can be faked, stolen, copied, or replaced. But boimetrics must be done without using a computer or converting them to digital form, or they will be as easy to defraud as the man made items, because the digital copy itself is man-made.