Due to the continuous developing of the sniffing technology, our network is facing unprecedented dangers. Software based on the sniffing technology, or commonly called “sniffer”, can intercept and analyze the packets transmitted on the network so as to illegally get sensitive information transmitted around the network. They are passive, quiet and uneasy to be detected by firewalls or IDS (intrusion detection system). In today’s network, data are commonly transmitted in plaintext which is the favorite food of sniffer software, such as emails and FTP transmission. How can we be aware of such a leak in our network? Well, the same sword can also be used to protect ourselves. We can monitor and test the transmission with a sniffer and fix the leak as soon as we find it so as to ensure the security of our network. Picture 1 is an example of captured account name and password by Colasoft Capsa (Pic. 1 Captured Account and Password by Colasoft Capsa) It’s not difficult for us to find out that the email is transmitted in plaintext in which format secrete information can be easily stolen. In order to ensure the security of our network, for example, our emails, we can encrypt it before we send it out. Even if it is captured by a sniffer, all it can see are garbled characters. The use of encryption in network transmission is the precondition of a secure network. We need to monitor and test the network application and encrypt which works in plaintext in order to ensure the security of network applications.