In the paper, we address oracle attacks for integrity watermarking in a communication setting. We show how an integrity verification algorithm can be modified in order to counteract an oracle attack. As an alternative to set up suitable communication protocols, we propose to counteract oracle attacks modifying integrity verification algorithms by adding a suitable temporal constraint. Categories and Subject Descriptors H.m [Information Systems]: Miscellaneous General Terms Security, Verification Keywords Covert channel, integrity watermarking, oracle attack, security, semi-fragile watermarking