In this paper, we present the modern approaches to building secure systems which are based on overcoming the problems resulting from asynchronization between system modeling and development on the one hand and modeling and development of the system security on the other hand. We also present the bases and solutions on which the idea of symbiosis is founded: a useful, close, permanent unity that combines languages for modeling systems with languages for modeling security. In this paper, we also present the design of one Web ecommerce application written by means of SecureUML-template and extended by being connected with protection against attacks (such as Web site defacement) and by the use of digital signature.