The recent development of the computer network technology has brought us many benefits including the electronic business. But also, one serious side effect is the explosive increase of the unauthorized computer access, and it becomes a big social problem. Of course, there are many security solutions in the market, but they cannot stop such intrusions or reduce the damages resulting from such accident. Besides, the protection of the system requires significant amount of the budget. Therefore, we need to think of minimizing damages or avoiding from the intrusions. One possible solution might be providing a training system to the system managers who are in charge of maintaining and protecting the servers. In this paper, we are suggesting a simulated security training system in the virtual learning environment. The system is being built based on the ITS structure primarily, and mainly focused on providing the simulated security exercises adaptively. For instance, since the system maintains the solution paths, the student’s problem solving steps are monitored and being interrupted with advising messages when necessary. It is designed as a client/server environment, so the student needs only the web browser to access the system. And the student can execute the selected task in the Java applet-based virtual OS environment according to the learning scenario.