Most people know of computer viruses. You should always have an anti-virus system running. It should have updated virus signature files downloaded daily for broadband and weekly for dialup connections. You should not have more than one anti-virus system active at any one time.
Many of you have probably heard of the recent viruses that caused havoc on the internet: Blaster, Welchia, Slammer, CodeRed, Nimda, and, most recently, Swen. While these can cause damage to your computer if you get infected, there are some simple steps you can take to greatly reduce your chances of infection.
First: what is a virus and how does one get infected?
A virus, much like the medical term, is a bit of software code that is self replicating. It need not do anything harmful or malicious, it just needs to reproduce itself. Some viruses attach themselves to the first sectors of Floppy disks, which is automatically read when you open a floppy. Most these days come through the internet. A virus is unique in that it infects other files, and then gets passed along with them, much like a virus infects a cell in your body. A virus doesn't necessarily need a security hole to work- as you can be the one who starts it spreading. There are different types of viruses, named after the different ways in which they operate and which files they infect. All operate in a similar manner.
Another common malicious program, often labeled a virus by the mass media, is a worm. The difference between worms and viruses is subtle, but a good description is this: worms tend to break into computers and focus on spreading themselves to other computers as rapidly as possible. Viruses tend to sneak in, while worms tend to force their way in. Worms often work their way into a computer without any user action necessary. Thus, Blaster is technically termed a Worm, as it broke into computers through a hole in Windows and ran itself and spread to other computers automatically.
What is believed is the most common malicious code is what is termed a 'Trojan Horse'. Much like the legend, a computer trojan is a program that pretends to be one thing but is actually another, tricking the user into running it. Note that a trojan is harmless until you open it; it can't infect you automatically. Many trojans open back doors to your computer so that crackers can get into your system and use it for various things, like sending spam across the internet.
Note that the types of program aren't defined by what sort of damage they do, but by how they infect computers and how they spread. One type is not intrinsically worse than another, and all of them can do things such as delete all of your files, pop up annoying messages, or make your computer run more slowly.
So, you might be asking- how can I protect myself?
1) Run an Antivirus program, and keep it up to date!
Several companies produce anti virus products. While some are getting better at detecting new viruses automatically, they aren't truly effective until the data file that stores information about known viruses includes the virus to protect against. Thus, it is imperative that you update your 'virus definitions' often, and immediately after a major virus/worm/trojan is released.
Here are some of the better AV products.
Symantec/Norton Antivirus: http://www.symantec.com/nav/nav_9xnt/
Kapersky AV: http://www.kaspersky.com/buyonline.html?info=25
Nod32 : http://www.nod32.com/home/home.htm
Panda AV: http://www.pandasoftware.com/
McAfee Virusscan: http://us.mcafee.com/root/package.asp?pkgid=100
AVG Anti-Virus (Free version available) http://www.grisoft.com/
Of those listed, Norton is the most popular. Many security junkies swear by Kapersky or Nod32. AVG is liked by many as it has a free version.
An antivirus program will automatically scan files on your computer as they are opened and modified, and isolate them from the rest of your system if they become infected. In this way you are protected. Note that they are not 100% effective, so you need to take some additional steps to help:
2) Update Windows often!
The blaster worm and almost all worms use vulnerabilities to spread. A patch for windows was out 25 days before blaster broke. Had you installed the patch, you would have been protected. Windows XP can automatically download updates and then prompt you to install them if you want, which keeps you from having to check all of the time. If you want, you can always use http://windowsupdate.microsoft.com
to check for updates (this works for all version from win98)
3) Don't open files from people you don't know, and don't open email attachments that you aren't expecting.
Many worms and viruses will harvest a list of all of the email addresses in your address book and then send a copy of themselves to those addresses. If someone sends you an attachment via email and you weren't expecting it, don't open it until you ask them if they meant to send it. If you get an attatchment from someone you don't know, don't open it. Swen, an email virus, pretends that it is a patch from Microsoft. Note that most antivirus programs can scan email as it arrives, which will help some what.
If you believe you are infected with a virus, don't go out and buy an AV program. Installing new programs can sometimes cause the virus to do more damage before you can get at it. Several AV companies are now offering free internet scans, which allow you to see if you are infected.
Here are a few of the free online scanners available:-
but others may be available via http://www.google.com
(PS Just don't use StopSign which has links to spyware).
Most of the section on Anti-Virus was written by ryri a DellTalk
regular with some small changes by myself .