  Arbitrated quantum signatures (AQS), for signing quantum message, have been
proposed. It was claimed that the AQS schemes could guarantee unconditional
security. However, in this paper, we show that all the presented AQS protocols
are insecure if quantum one-time pad encryption is used where the signer Alice
can always successfully acquire Bob's secret key and disavow any of her
signatures. The detailed attack strategies and security analysis are described.
Furthermore, the original version of the protocols is revised and accordingly
the security of the AQS protocols are improved. And meanwhile we present a
method to against Alice's disavowal proposed by Gao et al. (arXiv:1106.4398v1).
