When you are surfing the global network uses opens a number of ports. The most of software applications are intended for using of fixed port. As you can see on this picture Interne Explorer uses 80 port. Mail delivery applications such as Outlook and The Bat! use 25 and 110 ports. If you install Emule it will open 4662 and 4672 ports. Thus I computer is not secure because every application can open any port and transmit data by way of it. Besides, any external application also can connect to these ports. For example, I-Worm.MyDoom trojan can infect you PC. It opens 3127 port and hand over your private information. To reduce this threat and to monitor all ports there is some special applications. To reduce such thread you should close ports that you don’t need. There is some ways to it. For example to use Windows Worms Doors Cleaner. It is easy to use but it gives an opportunity to close only 135-139, 445 and 5000 ports. But to set up more reliable protection you should use special applications such as Firewalls. In next posts I’ll describe how to reduce this threat by means of such firewalls as Outpost Firewall, Kaspersky Internet Security, ZoneAlarm PRO, Comodo Firewall and Kerio Personal Firewall
PS Here you can see the list of common ports and to check them.