1 What is a computer virus? Computer program Replicating Problematic "Event" Types Detection and prevention

2 What is a computer virus? A computer virus is an executable program. By definition, a virus program is able to replicate itself. This means that the virus multiplies on a computer by making copies of itself. This replication is intentional; it is part of the virus program.

3 What is a computer virus? A virus can be introduced to a computer system along with any software program. For Internet users, this threat can come from downloading files through FTP (file transfer protocol). When a virus is introduced to a computer system, it can attach itself to, or sometimes even replace, an existing program. Thus, when the user runs the program in question, the virus is also executed. This usually happens without the user being aware of it.

4 What is a computer virus? A virus program contains instructions to initiate some sort of "event" that affects the infected computer. Each virus has a unique event associated with it. These events and their effects can range from harmless to devastating. For example: An annoying message appearing on the computer screen. Reduced memory or disc space. Modification of data. Files overwritten or damaged. Hard drive erased.

5 What is a computer virus? There are many types of computer viruses including file viruses, boot sector viruses and Trojan Horse programs. File virus - Most viruses fall into this category. A virus attaches itself to a file, usually a program file. Boot sector virus - These viruses infect floppy and hard drives. The virus program will load first, before the operating system. Trojan Horse - These programs appear to be something other than what they are, for example a "virus" that is disguised as a legitimate software program. Some virus experts do not classify Trojan Horse programs as true viruses, because they generally don't replicate.

6 What is a computer virus? Often, a user isn't aware that his or her computer is infected with a virus until the virus executes its unique event, such as displaying an unusual message or damaging a file. It is hard for people to detect viruses because they usually don't display symptoms prior to the event taking place. However, some viruses will provide early clues that they exist, such as: Changes in file or date stamp. Longer times to load programs. Slower system operation. A program fails to start. An unusual amount of disk activity (the floppy or disk drive runs for no apparent reason).

7 What is a computer virus? Using anti-virus tools makes detecting and eradicating viruses an easier task. There are many types of anti-virus software, employing several technologies. A common type of anti-virus tool is a "scanner". Scanners examine every file on a specific disc drive, looking for known virus "signatures". Every virus has a unique signature, which is a string of software code. Drawbacks to scanners include their inability to detect new viruses, and the requirement that the user determines when to initiate the virus scanning process. Other types of anti-virus tools include those that will run continuously on a system, and those that will run every time the machine is booted.

8 What is a computer virus? In Summary: A computer virus is an executable program that is able to replicate itself. Each virus contains instructions to initiate a unique, problematic event on the infected computer. The effects of these events can range from annoying to potentially devastating. A common type of virus is a file virus, which attaches itself to an existing program. When the program is run, the virus is also executed. Internet users can unknowingly download a software program that contains a virus. Other virus types include boot sector viruses and Trojan Horse programs which some experts do not classify as true viruses. Anti- virus tools can help a user to detect and eradicate viruses before they have an effect on an infected computer.