Firewalls

A firewall is a software or hardware device to protect your computer against hackers.

It watches the thousands of communication ports your Internet connection has, and alerts you if unauthorised traffic is detected.

Good firewalls watch not only for dangerous incoming messages, but also watch for unauthorised outgoing messages, such as those from Trojan Horses that have found their way onto your system.

"Trojans" are hacking programs installed by stealth onto your computer: they allow remote access to hackers who can access anything on your computer or control your computer remotely. Distributed denial-of-service (DDOS) attacks on Internet sites often use infected  "slave" computers to carry out the DDOS bombardment on the target sites and bring their servers to a halt. The users of the enslaved computers would not even know their computer was being hijacked - until ASIO secret service agents came knocking at their door - unless they had a firewall that would detect and block the unauthorised Internet activity.

If you have a cable connection to the Internet you probably have a static IP address, and a firewall is virtually compulsory. If, however, you use a dial-up modem connection to your ISP, you will get a differerent IP address every time you connect, so it is harder for hackers to determine your location. Even on a dial-up connection, however, it is alarming how soon you will find someone trying to do a "port probe" to see if your computer is vulnerable.

Firewalls also prevent hackers "port scanning" your computer to see if they could get in and plant or activate a Trojan. Firewalls would also prevent viruses sending your passwords or documents to a remote hacker.

Cartoon by Stephan Pastis (http://www.unitedmedia.com/comics/pearls/archive)

Want to see how the functions of your 65,536 internet ports are assigned?

How firewall stuff works

Also see Worms | Trojan Horses | Spyware | Viruses