Microsoft invests more than 1 billion USD per year in cybersecurity. In addition to the products and corresponding architectures, cybersecurity specialists work in the Micrsosoft Services to enable our customers to make their IT-system more secure. Or, in the event of a compromise, recapture it. The presentation will report on the experiences we gain from a large number of customers. These are big or small mistakes, misconceptions or simply conveniences that lead to near-disaster. We will also discuss how keylearnings are incorporated into main conceptual paradigms, like "assume breach" and some proposals to tackle those issues.