Data surveillance techniques are presented for the detection of security and/or performance issues on a zero-trust computer network. There is a network device policy manager that works in conjunction with a network data policy manager and which is in charge of performing the above data surveillance. Of special interest are those security issues where privileged data may be stolen by steganographic, data manipulation or any form of exfiltration attempts. Such attempts may be made by rogue users or admins from the inside of a network, or from outside hackers who are able to intrude into the network but can impersonate themselves as legitimate users. The above data surveillance techniques are also applied for detecting intentional or unintentional exfiltration/leak of privileged data/assets between unauthorized users/groups of the organization.