Unique Identification Authority of India (UIDAI) has warned that all 12-digit numbers "aren't Aadhaar" and recommended steps to verify before accepting them as identity proof. To verify the number, visit 'Verify an Aadhaar Number' page on UIDAI website, enter the 12-digit number and enter the security code or Captcha. The number's authenticity will appear after clicking on 'Proceed to Verify'.