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Today, Chief Executive Officer (CIO) duties are extended toward information systems auditing. Nowadays, CIO has to understand need for information systems auditing and know methods for its accomplishment. One of such methods is Benford's Law. In this work it will be described how this law can be used in information systems auditing for different purposes, e.g. in examination of some phenomena or eventually for fraud detection. Statistical measure will be described for identification if Benford's Law is valid for certain number set. It will be identified what are necessary characteristics that CAAT tool should support, in order to base auditing tests on this law. Results in application of this law in information systems auditing in cross border payment system and stock price analysis on Zagreb Stock Exchange will be presented.