  Due to potential capability of providing unconditional security, arbitrated
quantum signature (AQS) schemes, whose implementation depends on the
participation of a trusted third party, received intense attention in the past
decade. Recently, some typical AQS schemes were cryptanalyzed and improved. In
this paper, we analyze security property of some AQS schemes and show that all
the previous AQS schemes, no matter original or improved, are still insecure in
the sense that the messages and the corresponding signatures can be exchanged
among different receivers, allowing the receivers to deny accepting the
signature of an appointed message. Some further improvement methods on the AQS
schemes are also discussed.
