Q. What is the difference between Viruses, Worms and Trojans?
A.Viruses, Worms and Trojans are 3 different types of malware which are commonly called Viruses by the general public. These three can be differentiated as under:

1) A Virus is malicious code which is designed to interfere with computer operation, record, corrupt, or delete data, or spread itself to other computers on your LAN and throughout the Internet, often slowing down networks and causing other problems in the process. The defining criteria for a virus is that it attaches itself to (or if you prefer infect) other files and programs. Some viruses delete files and programs from the computer, some reformat your hard disk and some of them display silly and annoying (text, audio, video). Viruses without physical assistance can not spread from one machine to another, they require your help.

2) A Worm is also malicious code which spreads by itself from one networked machine to another. It does not need a host file and this is what differentiates it from a Virus. A Worm, after entering a computer, tries its best to infect other computers. That is why many worm automatically email themselves to all contacts in the email address book. A Worm will generally spread faster than virus thats why the number of its victims is far more than victims of virus. Examples of Worms are Sasser, Nimda and CodeRed.

The difference in a nutshell: a Worm will attack your computer by itself, whereas a Virus requires you to install it by downloading it from the network or storage device.

3) Trojan. According to Greek legend, Greeks won the Trojan War with the help of a massive wooden horse which they made to hide themselves from their enemies. The Greeks had been attacking the Trojan city but had been unable to get in. They hid themselves inside the horse and left it in front of Troy. The Trojans took the horse into their city and so the soldiers hiding inside were able to open the city gates at night.

In technical terms an Internet Trojan horse is a malicious program that presents itself in an interesting or entertaining manner but it harms the computer (e.g a free game, beautiful screen saver, mp3 song etc). These software, like the Greek Trojan horse, have a hidden agenda. Trojan horse like viruses can delete programs or data from your computer and can dp useful work for hackers. Currently Trojans are used to steal passwords, send spam email or use your computer to attack others.

Viruses and Worms may include Trojans as their payload or the Trojan may be downloaded later on.

Q.How does a Firewall stop Worms? Does it need to be updated so that it knows about new worms?
A.Xnet Firewalls are stateful firewalls. They work on the network layer and transport layer (thats layer 3 and layer 4 for the more technical people out there) , not on the application level (layer 7). This is why they do not need to be updated to stop new worms.

The way a firewall stops Worms is by ensuring that all attempts to connect from the outside are rejected. This way all attacks, including Worms, Hackers etc. are stopped.

The above is a limited and simplified FAQ. A full and complete analysis of your situation and requrements will be much more complex. Security is never simple.