  In a previous study, we considered an information-theoretic model of code
evolution. In it, agents obtain information about their (common) environment by
the perception of messages of other agents, which is determined by an
interaction probability (the structure of the population). For an agent to
understand another agent's messages, the former must either know the identity
of the latter, or the code producing the messages must be universally
interpretable. A universal code, however, introduces a vulnerability: a
parasitic entity can take advantage of it. Here, we investigate this problem.
In our specific setting, we consider a parasite to be an agent that tries to
inflict as much damage as possible in the mutual understanding of the
population (i.e. the parasite acts as a disinformation agent). We show that,
after introducing a parasite in the population, the former adopts a code such
that it captures the information about the environment that is missing in the
population. Such agent would be of great value, but only if the rest of the
population could understand its messages. However, it is of little use here,
since the parasite utilises the most common messages in the population to
express different concepts. Now we let the population respond by updating their
codes such that, in this arms race, they again maximise their mutual
understanding. As a result, there is a code drift in the population where the
utilisation of the messages of the parasite is avoided. A consequence of this
is that the information that the parasite possesses but the agents lack becomes
understandable and readily available.
