Hope this helps you understand Viruses and what can be done

The most common types of viruses work through email, particularly Outlook Express. You can almost always avoid them by not opening attachments.
Other types of viruses infect the macro templates in Microsoft Word and Excel documents. These viruses also spread via email, or via documents that are shared on a corporate server. They can also spread when users exchange floppy disks.

Viruses are computer programs, and they can do virtually anything that any normal program can do. This includes deleting files, formatting a user's hard drive, and even overwriting the BIOS, completely disabling the computer.
The safest thing you can do to avoid viruses is to avoid opening email attachments.

You can also run antivirus programs, such as Norton AntiVirus, that contain "on-access" scanners. This type of scanner runs constantly in the background.
Every time a user copies a file to the hard drive, runs a program, or loads a document into a word processor or spreadsheet, the on-access scanner will automatically check to see whether the file contains a virus. This is completely transparent to users they are only notified if they have a virus.

Users should exercise particular care with programs they download from the Internet or exchange with others.
Some are as benign as the common cold, and others can be as deadly to your hard drive as something from the movie "Outbreak." We're talking computer viruses, and with more than 17,000 known strains, there's a pretty good chance your computer will eventually encounter one.
Take into account that only about 40 percent of PC owners use antivirus software, and that viruses can easily spread to your system from the Internet, bulletin boards, and email attachments, and we're talking epidemic. Luckily, it's easy to protect your computer from viruses and to cure it if it gets infected.

Typically, a computer virus will replicate itself and try to infect as many files and systems as possible. If your system is infected and you save a file to a disk, you will probably infect the disk and any system that uses the disk.
New computer viruses are being written all the time, so you need to know how your computer can be infected.
Here are some common symptoms of infection:
Unusual messages or displays on your monitor
Unusual sounds or music played at random times
Your system has less available memory than it should
A disk or volume name has been changed
Programs or files are suddenly missing
Unknown programs or files have been created
Some of your files become corrupted or suddenly don't work properly

There are several programs (called virus protection software, antivirus software, or virus checks) that will check your system for known viruses, scan incoming files, and warn you before any infected files are let in.
These programs are only as good as their database of virus definitions. Since new viruses are being introduced all the time, antivirus definitions need to be updated often. You should set your antivirus program to automatically update so you never fall behind on your virus definitions.
We recommend either installing Norton AntiVirus or using a free online virus scanner called housecall.antivirus.com.

Once you've scanned your system for viruses, you should follow certain rules for keeping your system clean. First, be careful whenever you're opening attachments or downloading files. If you like to open attachments, you should install an always-on antivirus application such as Norton AntiVirus. Also, before you open any attachment, examine its file extension. Be very wary of any attachment with an extra extension, such as "happyfun.jpg.vbs."
We strongly recommended that you set up your software to automatically scan for viruses 100 percent of the time. This is the most important thing you can do to protect your system. Doing this will make your system take a little longer to boot up, but it's worth the extra wait. It's also extremely important that you keep your antivirus software current. You should regularly check for software updates, usually at the vendor's website

What to do if you have a virus

If your virus protection software detects a virus on your computer, try to get the software to clean or disinfect the system. If this doesn't work, a program such as Norton AntiVirus will place all the infected files it finds inside a quarantine.

In extreme cases, you may need to reformat your hard drive, destroying all the data on it. Then you'll have to reinstall your software and data, assuming you have the original software disks and clean backups of your files. In this case, you should install your virus protection software on the empty hard drive so you can verify that your backup files and original software are virus-free.
You might also want to contact all the people you've recently exchanged information with -- via floppy disks, email attachments, Zip disks, or CD-R disks -- and let them know that your system's been infected and theirs may be infected as well. Tell them what symptoms to look for or the name of the virus.

Antivirus software pages
Antivirus software manufacturers
Free virus scanners

*Links below*

Symantec Antivirus Research Center

Virus Bulletin

Virus Help and Information

Computer Virus Information

Symantec (Norton)

Mcafee

Trend Micro

Computer Associates

PC Pitstop