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What Are Computer Viruses

Computer viruses are software programs that invade a computer system to wreck havoc with computer files or the computer users themselves. Some are benign causing nothing more than a nuisance while others can delete files or even destroy computer hardware. Typically viruses are programmed to reproduce themselves and spread from one computer system to another, just like a normal human virus spreads via human contact throughout the population. Computer viruses can be spread via diskettes or other removable media, by way of email attachments, or in some cases simply by being connected to the Internet and not protected.
Types of
Computer Viruses

Computer viruses are categorized into four main types: boot sector, file or program, macro, and multipartite viruses.

Boot sector viruses are usually transmitted when an infected floppy disk is left in the drive and the system is rebooted. The virus is read from the infected boot sector of the floppy disk and transferred to the master boot record of the system's hard drive.  Then, whenever the computer is booted up, the virus will be loaded into the system's memory. Any floppy disk formatted as a bootable disk in the infected machine would contain the virus and spread itself to other machines.

Program or file viruses are software programs that attach themselves to executable programs. Once the infected program is run, the virus is transferred to your system's memory and may replicate itself further. It may spread to all the files on a hard drive or to files of a specific type. Common viruses such as Happy99, Pretty Park, and the ILOVEYOU worm can be classified as this type.

Macro viruses are currently the most commonly found viruses. They infect files run by applications that use macro languages, like Microsoft Word or Excel. The virus looks like a macro in the file, and when the file is opened, the virus can execute commands understood by the application's macro language. The infamous Melissa virus is a macro virus as well as the common Laroux Excel spreadsheet virus.

Multipartite viruses have characteristics of both boot sector viruses and file viruses. They may start out in the boot sector and spread to applications, or vice versa.

How Does A Virus Infect Your Computer

Years ago, only certain types of files (generally executable files like program files) could be carriers of a virus, however with the invention of macro languages in programs like Microsoft Word or Excel, and the use of Javascript in web page building, almost any type of data could theoretically carry a virus. The most common way a computer is infected with a virus today is through the use of a floppy disk containing data from another computer, or through the use of the Internet with email, IRC, or other online communication.

Because viruses are becoming more clever, no one should be using a computer that does not have anti-virus software running on it. The more you use a computer, the more likely it is you will encounter a virus.

Some common symptoms that could indicate your system's been infected are:

  • Computer slows down without reason
  • 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
What to Do If Your Computer Is Infected With A Virus

If you're system is infected with a virus, you should install anti-virus software to rid it of the intruder. You can visit PC Hell's Virus Center for Tips on Virus Prevention and Cures. If the anti-virus software can't clean the system, you may  have to delete the infected files from your system and restore from backups.

In extreme cases, it may be necessary to reformat your hard drive, destroying all of 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, it's a good idea to install your virus protection software right after installing your operating system (like Windows), so that the integrity of your backup files and original software can be verified.

You might also want to contact all the people that you've recently exchanged information with -- via floppy disks, e-mail attachments, Zip disks -- and let them know your system's been infected and theirs may be infected as well. You'd want to advise them to check their system for the appropriate virus or symptoms.

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Buy Anti-Virus Software

If you don't already have antivirus software loaded on your computer. You should download and install an antivirus product immediately. The popular commercial antivirus products like McAfee and Norton are ok, but there are also excellent free antivirus solutions available. Listed below are some of the popular free and commercial antivirus software products.

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