  Harnessing quantum processes is an efficient method to generate truly
indeterministic random numbers, which are of fundamental importance for
cryptographic protocols, security applications or Monte-Carlo simulations.
Recently, quantum random number generators based on continuous variables have
gathered a lot of attention due to the potentially high bit rates they can
deliver. Especially quadrature measurements on shot-noise limited states have
been studied in detail as they do not offer any side information to potential
adversaries under ideal experimental conditions. However, they may be subject
to additional classical noise beyond the quantum limit, which may become a
source of side information for eavesdroppers. While such eavesdropping attacks
have been investigated in theory in some detail, experimental studies are still
rare. We experimentally realize a continuous variable eavesdropping attack,
based on heterodyne detection, on a trusted quantum random number generator and
discuss the limitations for secure random number generation that arise.
