  This article discusses opportunities and challenges of physical layer
security integration in massive multiple-input multiple-output (MaMIMO)
systems. Specifically, we first show that MaMIMO itself is robust against
passive eavesdropping attacks. We then review a pilot contamination scheme
which actively attacks the channel estimation process. This pilot contamination
attack is not only dramatically reducing the achievable secrecy capacity but is
also difficult to detect. We proceed by reviewing some methods from literature
that detect active attacks on MaMIMO. The last part of the paper surveys the
open research problems that we believe are the most important to address in the
future and give a few promising directions of research to solve them.
