I happened to learn that there is an actively researched IT-security field named network steganography. Could experts give a short overview of the current state of affairs, especially about the extent of risks therefrom as well as the counter-measures already being taken and also about eventually feasible usages of the techniques there for beneign purposes by the common people?
[Addendum] I just found a new book: W. Mazurczk et al. (Eds.), Information Hiding in Communication Networks. Wiley, 2016.