As the ontologies are the pivotal element of the Semantic Web in E-Commerce, it is necessary to protect the ontology´s integrity and availability. In addition, both suppliers and buyers will use an ontology to store confidential knowledge pertaining to their preferences or possible substitutions for certain products. Thus, parts of an ontology will need to be kept confidential. We propose to use well establishedstandards of XML access control. E-commerce processes require the confidentiality of customer information, the integrity of product offers and the availability of the vendors´ servers. Our main contribution-the introduction of a Security Ontology-helps to structure and simulate IT security risks of e-commerce players that depend on their IT infrastructure.