Computer Virus Information
Computer viruses are malicious programs (or sets of instructions) which are designed to replicate themselves from machine to machine. Viruses may evolve over time if they are designed to change their own content as they replicate or if they are changed by someone who has access to the code. Viruses may also contain destructive code. These programs are generally designed to make changes to software that already exists on the system thus enabling them to replicate themselves, display messages, destroy data or software, or inhibit access by the user of the system.
Computer viruses can be a serious threat to an organization since they usually result in lost time and effort required to clean and restore infected systems. Viruses are a threat because:
- Viruses can quickly spread to a huge number of computer systems or networks.
- Because access to computer and communications hardware, especially in the personal computing environment, means that virtually anyone could introduce a virus, intentionally or without knowing, to the environment.
- Viruses can mutate as a result of an individual adding code to an existing virus or if they are designed to change themselves as they propagate through an environment. Such mutations may result in viruses that are more harmful and more difficult to detect and eliminate.
- Although techniques for detecting and correcting known viruses have been developed and are relatively cheap to acquire, the problem will not disappear since not everyone protects and monitors their system or takes steps necessary to prevent infection. The techniques for detecting and correcting future viruses will depend on the nature of such viruses.
How can you tell if your machine is infected?
Recognizing that a system is infected by a virus depends on the type of virus itself. Some examples of known viruses and their effect include:
- The Stoned Virus: One version of this virus randomly displays the message "Your PC is stoned." on the screen.
- Ping Pong Virus: This virus plays a Ping Pong game on your screen.
- Cascade Virus: This virus manifests itself by randomly dropping characters from your screen to the bottom of the screen creating a pile of letters at the bottom.
Some viruses, most notably "stealth" viruses, hide themselves on a system and are triggered on a specific date, for example the Friday the 13th Virus. Some viruses may result in slower response time as they tie up your system's resources. Others can prevent you from accessing files by altering directories and file tables.
How can a machine become infected?
The PC environment is not controlled like a mainframe computer environment. Sharing of Personal Computers, MACs and diskettes is quite common. There are a number of ways in which a machine can become infected, including:
- Use of an infected diskette on a machine (infected diskettes are the most common way viruses are spread from machine to machine.)
- Shareware software or software downloaded from a Bulletin Board may be infected.
- Pirated computer games are frequently infected. Beware of copies of games kids get from their friends!
What should you do if you suspect that a virus has infected your machine?
- DO NOT attempt to remove the virus unless you have a virus detection and cleaning program installed on your computer. Stop using
your machine and make sure that the infected machine and any media used on the machine are isolated until the problem is solved.
What can you do to prevent your machine from becoming infected?
There are some very basic things you can do to prevent viral infections. Safe computing is relatively easy to achieve. The following guidelines will help you practice safe computing:
- Back up your files regularly (at least weekly). Make separate backups of your data files and your software and store your backup diskettes in a safe and secure place away from your machine. Backups may be the only way to recover infected systems.
- Do not use illegal or "pirated" software on your machine.
- Do not use shareware programs unless you are absolutely sure that the programs are free of viruses.
- If you download programs from Bulletin Boards, scan them for viruses before you use them.
- When you get new software for your machine, make sure it is shrink-wrapped and check the diskettes before using them on your computer.
- Make sure that your diskettes with software programs on them are write-protected. This prevents viruses from being copied onto the diskettes.
- If your "new" machine is in reality a recycled one that someone else used before, ask the individual installing your machine to do a "low-level format" of the hard drive. This will destroy any viruses that may be on the hard drive as well as get rid of illegal copies of software.
- If you "new" machine comes pre-loaded with software or if the hard drive is pre-formatted, scan the hard drive for viruses before you start using the machine.
- If you are sharing diskettes with someone else or if you use your diskettes on someone else's machine or a machine which is part of a "Pool", scan your diskettes before using them on your machine.
- If your know that your machine or any of your diskettes are infected or if you suspect a viral infection, do not use your diskettes on another PC. Your diskettes are most probably infected too and all you will accomplish is to spread the virus and infect someone else's machine!
- Do not boot your machine with a diskette that has not been scanned for viruses even if you think the diskette only contains data. Never booth your machine from a diskette created on another machine.
- If you normally boot your machine from the hard drive, make sure that there isn't a diskettes in your
- If your machine is located in an open office area or if the machine is used by more than one individual, consider installing a security package that restricts the use of the machine to authorized users.
- Public-domain software should not be used until it is tested and labeled "clean".
- All software should be acquired from reputable dealers. Non-shrink-wrapped software may be infected although there are known incidents involving spreading of viruses through shrink-wrapped software.