Almost all Trojans and worms need an access to network, because they have to send data out to the hacker. Only the useful data are sent to the attacker the Trojan accomplishes its mission. So it should be a good solution that we start from the aspect of traffic analysis and protocol analysis technology. We are going to detect the Trojan horse and worm with the help of a network analyzer-Colasoft Capsa. Capsa is an easy-to-use and intuitive network analyzer, which provides enough information to help check if there is any Trojan activities in our network. In this article I’m going to show you how to spot a Trojan or worm.