A Computer virus is a program (or a piece of software), which attaches itself to another program or a system.
It is designed specifically to copy itself to other programs and cause some undesirable effect on the programs (or damage them) without the knowledge of the user.
For example, it may attach itself to the FORMAT command, and be run every time you format a diskette.
A virus is a computer code usually designed to carry out 2 tasks;
(i). To replicate (duplicate/copy) itself from one computer system to another.
(ii). To locate itself within a computer system making it possible for it to amend/ destroy programs and data files, by interfering with the normal processes of the Operating system.
The program is written by people who are cruel, unethical and malicious.
Risks Posed By Computer Viruses
The risks posed by viruses and the primary impacts of a virus attack can be classified into two categories;
1). Destructive viruses.
Massive Destruction
The virus attacks the format of disks, or Delete all files on the disk making any damage on programs or data on that disk unrecoverable.
Partial Destruction
The virus erases and modifies a specific portion of a disk affecting any files stored in that location.
Selective Destruction
The virus erases and modifies specific files or file groups.
2). Non-destructive viruses.
These viruses do not cause any destruction, but are usually annoying.
What Non-destructive viruses do?
1. They might lock the Keyboard.
2. Change keystroke values (e.g. changing the effect of the SHIFT key).
3. Display an obnoxious (loathsome/ horrible/ intolerable) message on the screen.
4. Change the display colours.
Sources of Computer Viruses
The most common sources of virus transmission are;
(a). Contact with contaminated systems.
Any disk used on a contaminated system could become contaminated. If the same disk is used on another system, then the virus will spread.
(b). Pirated Software.
It is designed specifically to copy itself to other programs and cause some undesirable effect on the programs (or damage them) without the knowledge of the user.
For example, it may attach itself to the FORMAT command, and be run every time you format a diskette.
A virus is a computer code usually designed to carry out 2 tasks;
(i). To replicate (duplicate/copy) itself from one computer system to another.
(ii). To locate itself within a computer system making it possible for it to amend/ destroy programs and data files, by interfering with the normal processes of the Operating system.
The program is written by people who are cruel, unethical and malicious.
Risks Posed By Computer Viruses
The risks posed by viruses and the primary impacts of a virus attack can be classified into two categories;
1). Destructive viruses.
Massive Destruction
The virus attacks the format of disks, or Delete all files on the disk making any damage on programs or data on that disk unrecoverable.
Partial Destruction
The virus erases and modifies a specific portion of a disk affecting any files stored in that location.
Selective Destruction
The virus erases and modifies specific files or file groups.
2). Non-destructive viruses.
These viruses do not cause any destruction, but are usually annoying.
What Non-destructive viruses do?
1. They might lock the Keyboard.
2. Change keystroke values (e.g. changing the effect of the SHIFT key).
3. Display an obnoxious (loathsome/ horrible/ intolerable) message on the screen.
4. Change the display colours.
Sources of Computer Viruses
The most common sources of virus transmission are;
(a). Contact with contaminated systems.
Any disk used on a contaminated system could become contaminated. If the same disk is used on another system, then the virus will spread.
(b). Pirated Software.
The use of rented disks containing Pirated computer software introduces the risk that the software may be contaminated by a virus code or might have been amended to perform some other destructive function, which may affect your system.
(c). Infected Proprietary Software.
There are cases of virus programs being introduced and contaminating software under development in laboratories and then being installed onto disks containing the finished software product.
(d). Updates of Software distributed using Networks.
Distribution of software through networks is an obvious target for virus programmers as they provide a built-in method for widespread and anonymous (unidentified, unknown, secret) propagation.
Symptoms of a Computer with Virus.
The presence of a virus can be indicated if one or more of the following symptoms appear on your computer.
(i). Unfamiliar graphics or quizzical (surprising) messages appearing on the screen.
(ii). Programs taking longer than usual to load.
(iii). Disk access time seeming too long for simple tasks.
(iv). Unusual Error messages occurring more frequently.
(v). Less memory available than usual.
(vi). Access lights turning on for non-referenced devices.
(vii). Programs or files disappearing mysteriously.
(viii). Executable files or data files changing size for no obvious reason.
(ix). Changes of disk volume IDs.
(x). Frequent Read/Write errors.
(xi). Computer hags (gets stuck) anytime when executing or running a program.
Any evidence of these or similar events should be of an immediate concern. The PC should be isolated at once and investigated.
Prevention against Viruses (Ways to avoid viruses).
The following steps should be followed to prevent virus infection;
(i). Never accept software from anyone.
(ii). Never download software from Internet.
(iii). If possible, avoid using one disk on several machines.
(iv). Scan all boot disk using an up-to-date Anti-virus program
(v). Practice protection rules with your computer.
Detection and Removal of Viruses.
Use Anti-virus software to detect infected files and remove known viruses.
Some commonly used terms.
Trojans: - They are programs, which deliberately set out to destroy your data. Their trigger (activator / starter) could be time (time bombs) or certain logical condition (logic bombs).
Variants: - Are programs very similar to virus codes and go by the same virus family name but give slightly different effects.
Worm: - A program that „borrows‟ (or sneaks) into a computer’s memory. It is designed to search for idle computer memory, and then rewrite itself successfully through the computer’s memory until the system crashes.
(c). Infected Proprietary Software.
There are cases of virus programs being introduced and contaminating software under development in laboratories and then being installed onto disks containing the finished software product.
(d). Updates of Software distributed using Networks.
Distribution of software through networks is an obvious target for virus programmers as they provide a built-in method for widespread and anonymous (unidentified, unknown, secret) propagation.
Symptoms of a Computer with Virus.
The presence of a virus can be indicated if one or more of the following symptoms appear on your computer.
(i). Unfamiliar graphics or quizzical (surprising) messages appearing on the screen.
(ii). Programs taking longer than usual to load.
(iii). Disk access time seeming too long for simple tasks.
(iv). Unusual Error messages occurring more frequently.
(v). Less memory available than usual.
(vi). Access lights turning on for non-referenced devices.
(vii). Programs or files disappearing mysteriously.
(viii). Executable files or data files changing size for no obvious reason.
(ix). Changes of disk volume IDs.
(x). Frequent Read/Write errors.
(xi). Computer hags (gets stuck) anytime when executing or running a program.
Any evidence of these or similar events should be of an immediate concern. The PC should be isolated at once and investigated.
Prevention against Viruses (Ways to avoid viruses).
The following steps should be followed to prevent virus infection;
(i). Never accept software from anyone.
(ii). Never download software from Internet.
(iii). If possible, avoid using one disk on several machines.
(iv). Scan all boot disk using an up-to-date Anti-virus program
(v). Practice protection rules with your computer.
Detection and Removal of Viruses.
Use Anti-virus software to detect infected files and remove known viruses.
Some commonly used terms.
Trojans: - They are programs, which deliberately set out to destroy your data. Their trigger (activator / starter) could be time (time bombs) or certain logical condition (logic bombs).
Variants: - Are programs very similar to virus codes and go by the same virus family name but give slightly different effects.
Worm: - A program that „borrows‟ (or sneaks) into a computer’s memory. It is designed to search for idle computer memory, and then rewrite itself successfully through the computer’s memory until the system crashes.
