I follow the ethical principles of the Association of German Professional Psychologists (BDP):
Psychologists must strive at all times to ensure that their professional conduct complies with the very highest standards of ethical responsibility. They are not only committed to respecting the rights of those with whom they work, but also, whenever appropriate, to intervening actively to protect such rights.
Psychologists are required to protect the confidentiality of all information confided to them in the course of exercising their professional activities except in those exceptional instances defined by law or in the event that other higher-ranking legal interests are in jeopardy.
Psychologists may only collect, store and use data about clients/patients which is relevant to the services provided.
Complete Ethical Principles in English: http://www.bdp-verband.de/bdp/verband/ethic.shtml