Currently, there are three common Trojans: positive-orientation connection Trojan, rebounding connection Trojan, mail receiver Trojan.

Positive-orientation connection Trojan, what’s so-called positive-orientation? The Trojan infector starts a port on the machine, and we go and connect his port. We should know his IP then we could connect him. 123 is the started port on his machine.

As till now, the popularity of bandwidth Internet (dynamic IP) and router, this software turns to be full of shortages.

Dynamic IP: each time to dial up, IP would change synchronously, so even if the opposite party is infected by the Trojan, next time dialing up, we could not get the Internet because of non IP could be found.

Router: several computers use one single bandwidth (Internet bar is the best classic example), they connect to the bandwidth by a router, for example, host IP is 225.124.3.41, while interior network (the machine using the router) IP is 192.168.x.x. In the environment of interior network, our exterior surrounding is inaccessible, even the machine is infected by Trojans. Simply speaking, interior network machines are much safer that outside could not access. We have no way to connect the interior network machine. While the machine connecting the interior, except in the same network (in the Internet bar, machine A could connect to the machine B with RIDMIN).


Summarization:

In different area networks, Positive-orientation connection Trojan could only connect to the machines in exterior network, but not the ones in