Certain aspects of the disclosure are directed to methods and apparatuses of intrusion detection for integrated circuits. An example apparatus can include a wired communications bus configured and arranged to carry data and a plurality of integrated circuits. The plurality of integrated circuits can include a first integrated circuit configured and arranged to operate in a scan mode during which the first integrated circuit performs a scan test to detect one or more faults in circuitry of the plurality of integrated circuits. The plurality of integrated circuits can further include a second integrated circuit configured and arranged to operate in a mission mode and supervise data traffic by monitoring communications including data patterns and accesses on the wired communications bus. In response to identifying a suspected illegitimate access, the second integrated circuit can perform a security action to mitigate a suspect illegitimate action in the plurality of integrated circuits.