Confirmer signatures are different from standard signatures in the sense that without the help and cooperation of a designated confirmer, a verifier cannot determine the validity of a confirmer signature. But except of the signer, anyone else (including the confirmer) can not generate a valid confirmer signature on behalf of the signer. At the same time, the confirmer cannot cheat verifiers once he is involved in the procedure of signature verification. Furthermore, if it is necessary, the confirmer could convert confirmer signatures into standard ones such that the validity of these converted signatures can be publicly validated. Wang et al. proposed an efficient new confirmer signature scheme based on DSA and RSA, and claimed that their scheme is secure. However, several serious security flaws in their scheme are identified so that their investigation does not succeed.