Multiple variants of essentially the same multiple-choice questions are generated, having similar appearance, but actually different answers. Any single test has at most one variant of any particular question for which multiple variants exist. Different versions of the test can be generated by changing the combination of question variants used. In one aspect, different versions of the test identified by different combinations of variant questions can be used to determine the source of an unauthorized leak of test questions. In another aspect, the responses of a test subject to variant questions can be analyzed for suspicious patterns, indicating possible unauthorized access to a previous test version.