Unlike a hand-written signature, the biometric fingerprint can be replicated without the will/knowledge of the owner. Any business can collect fingerprints and personal data. If fingerprints are leaked online or sold to mobile phone theives, then they can conduct Aadhaar-enabled financial transactions.
The UIDAI Act offers no recourse or alternative for those whose biometric data has been stolen. With so many things made dependent on Aadhaar, life will come to a nought for those people. Aadhaar is a single-point failure on which the financial security of our nation is being set to be wrecked.