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Test compression is widely used for reducing test time and cost of a very large scale integration circuit. It is also claimed to provide security against scan-based side-channel attacks. This paper pursues the legitimacy of this claim and presents scan attack vulnerabilities of test compression schemes used in commercial electronic design automation tools. A publicly available advanced encryption standard design is used and test compression structures provided by Synopsys, Cadence, and Mentor Graphics design for testability tools are inserted into the design. Experimental results of the differential scan attacks employed in this paper suggest that tools using X-masking and X-tolerance are vulnerable and leak information about the secret key. Differential scan attacks on these schemes have been demonstrated to have a best case success rate of 94.22% and 74.94%, respectively, for a random scan design. On the other hand, time compaction seems to be the strongest choice with the best case success rate of 3.55%. In addition, similar attacks are also performed on existing scan attack countermeasures proposed in the literature, thus experimentally evaluating their practical security. Finally, a suitable countermeasure is proposed and compared to the previously proposed countermeasures.