Breaking AntiSpam systems with parasitic spam

The existance of networks of 'bots' raises the possibility of a new type of spam that breaks the current paradigm of spam defense, in which the defence acts purely as a filter. This spam, which we call parasitic spam, looks to a filter very much like spam with scraped text, but contains instead legitimate content going from a legitimate sender to a legitimate recipient. In this problem statement, we will discuss what parasitic spam is and is not, the likelihood of parasitic spam appearing in the wild, and possible countermeasures.