Re: So how secure are 'biometrics'?
Yep, it doesn't matter what biometric is used or even if it is impossible to fool the reader. Biometric authentication is fundamentally the same as any other form..
During enrolment, the authentication server collects data about your authenticator. This may be your password (hash) a seed for a 2FA token, X.509 public key or the base sample data for the biometric (etc. etc.)
During authentication, credential data is collected from the user. This could be input via a keyboard, smartcard reader or some weird and wonderfulscanning device. This data is now a normal bob of data. It may be processed by the client before being sent to the authentication server for processing.
The server compares what it is given by the client to what it has got stored in some fashion. This comparison will result in either a positive or negative result. The authentication server doesn't give a damn about your fingerprint, iris scan or anal probe results, all it needs is a blob of data. If you can supply some data that it can match and inject it into the right place in the communications channel, the server will accept it.
That's why on many Windows networks if you have a password hash, it matters not that you don't know the password or if you have a 2FA token seed and the generation alorithm, you don't need the original token. if you have enough information about a biometric credential and the system in use, you don't need the actual body part and just bypass the scanner hardware.
In the password or 2FA examples, you can revoke the credential and issue a new one. Short of forced surgery, there is simply no way of doing this with biometrics.