What are computer viruses, worms, and Trojan horses?

Some tips for avoiding computer viruses

Computer viruses are programs or macros, not microorganisms, but they are infectious and can be highly complex. Viruses implant instructions in other programs or storage devices and can attack, scramble, or erase computer data. The virulence of computer viruses lies in their ability to replicate themselves and spread from system to system. Few computing systems seem to be immune to infection.

High-risk behaviors
The following activities are among the most common ways of getting computer viruses. Minimizing the frequency of these activities will reduce your risk of getting a computer virus:

• Freely sharing computer programs and system disks, or downloading files and software through file-sharing applications such as KaZaA
  
  
• Downloading executable software from public-access bulletin boards or Web sites
  
  
• Using your personal disk space (e.g., floppy disks) with public computers or other computers that are used by more than one person
  
  
• Opening email attachments without first scanning them for viruses.
  
  
• Opening any email attachment that ends in .exe , .vbs , or .lnk on a computer running Microsoft Windows

Signs of a virus infection
If your computer begins to act strangely, or if it stops being able to do things it has always done in the past, it may be infected with a virus. Symptoms such as longer-than-normal program load times, unpredictable program behavior, inexplicable changes in file sizes, inability to boot, strange graphics appearing on your screen, or unusual sounds may indicate that a virus is on your system. However, it is important to distinguish between virus symptoms and those that come from corrupted system files, which can look very similar. Remain calm and objective, and rule out more standard causes before suspecting a virus.

How to avoid computer viruses
Prevention is a matter of vigilance and avoiding contact with unknown disks. It is usually the unwary who get computer viruses. Following is a list of some recommendations for safe computing:

• The most important thing you can do to keep your computer safe is to install virus detection software. Antivirus programs perform two general functions: scanning for and removing viruses in files on disks, and monitoring the operation of your computer for virus-like activity (either known actions of specific viruses or general suspicious activity). Most antivirus packages contain routines that can perform each kind of task. One good virus protection software package is Norton/Symantec AntiVirus(NAV/SAV) for Windows and Mac OS computers.

  Note: Don't forget to keep your virus detection software updated! Virus patterns change all the time, and you must update your virus pattern files regularly for full protection.

• Keep your operating system current with the latest patches and updates. The writers of viruses and worms often exploit bugs and security holes in operating systems and other computer software. Software manufacturers frequently release patches for such holes.
  
• Back up your files. Viruses are one more very good reason to always back up your files.

  Note: If you back up a file that is already infected with a virus, you can re-infect your system by restoring files from the backup copies. Check your backup files with virus scanning software before using them.

• Keep your original application and system disks locked (or write-protected). This will prevent the virus from spreading to your original disks.
  
  
• If you must insert one of your application disks into an unknown computer, lock (write-protect) it first, and unlock your application disk only after verifying that the machine is virus-free.
  
  
• Obtain public-domain software from reputable sources. Check newly downloaded software thoroughly using reputable virus detection software on a locked floppy disk for any signs of infection before you copy it to a hard disk. This can also help protect you from Trojan horse programs.
  
  
• Quarantine infected systems. If you discover that a system is infected with a virus, immediately isolate it from other systems. In other words, disconnect it from any network it is on and don't allow anyone to move files from it to another system. Once the system has been disinfected, you can copy or move files.
  
  
• If you use a desktop version of Outlook, minimize use of the preview or reading pane feature.