Before revision: Multi-modal biometric systems are commonly believed to be intrinsically more robust to spoof attacks, but recent studiesZahid Akhtar, "Security of Multimodal Biometric Systems against Spoof Attacks" , (PDF).
After revision: Multi-modal biometric systems are commonly believed to be intrinsically more robust to spoof attacks but recent studiesZahid Akhtar, "Security of Multimodal Biometric Systems against Spoof Attacks" , (PDF).