The invention provides a data network, systems and methods for checking nodes of a data network that are used for detecting whether a privacy policy concerning an information is maintained. The information comprises a mark corresponding to the privacy policy. The mark defines the storage place or the accessing paths or the transferring paths of the information. The mark is automatically searchable. The mark is searched, analyzed and checked as to whether the privacy policy is maintained. The advantage of the system is that vulnerabilities of systems for protecting confidential information may be detected a long time before an attack on the confidential information occurs.