I have seen several academic sources mentioning covert channels in computers, such as one process sending data to another process/thread on the same machine in a way that attempts to avoid detection. Covert channels methods include for instance timing, resource contention... According to the Trusted Computer Security Evaluation Criteria, covert channels are
ways of transferring information from a higher classification compartment to a lower classification.
Is there an example of an actual malware having this behavior?
I am interested more in covert channels inside a single computer than network channels.