  The eavesdropping scheme proposed by W\'{o}jcik [Phys. Rev. Lett. {\bf
90},157901(2003)] on the ping-pong protocol [Phys. Rev. Lett. {\bf 89},
187902(2002)] is improved by constituting a new set of attack operations. The
improved scheme has a zero eavesdropping-induced channel loss and produces
perfect anticorrelation. Therefore, the eavesdropper Eve can safely attack all
the transmitted bits and the eavesdropping information gain can always exceed
the legitimate user's information gain in the whole domain of the quantum
channel transmission efficiency $\eta$, i.e., [0,100%]. This means that the
ping-pong protocol can be completely eavesdropped in its original version. But
the improvement of the ping-pong protocol security produced by W\'{o}jcik is
also suitable for our eavesdropping attack.
