  We investigate the security of continuous-variable (CV) quantum key
distribution (QKD) using coherent states in the presence of quadrature excess
noise. We consider an eavesdropping attack which uses a linear amplifier and
beam splitter. This attack makes a link between beam-splitting attack and
intercept-resend attack (classical teleportation attack). We also show how
postselection loses its efficiency in a realistic channel.
