  We propose a new kind of individual attack, based on randomly selected
dissipation, on Bennett-Brassard 1984 protocol of practical quantum key
distribution (QKD) system with lossy and noisy quantum channel. Since an
adversary with super quantum channel can disguise loss and errors induced by
his attack as that of the system, he can obtain innegligible amount of
information for a practical QKD system, without being detected by legal
participants.
