A computer virus is an executable program. Depend on the nature
of a virus, it may cause damage of your hard disk contents, and/or
interfere normal operation of your computer.
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.
In most cases, if a file that contains virus is executed or copied onto
another computer, then that computer will also be "infected"
by the same 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), or referencing
email attachments. (Please refer to our web page on
Handling Email's File Attachments for details.)
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.
A virus program contains instructions to initiate some sort of "event"
that affects the infected computer. Each virus has an unique event
associated with it. These events and their effects can range from
harmless to devastating. For examples:
- An annoying message appearing on the computer screen.
- Reduced memory or disk space.
- Modification of data.
- Files overwritten or damaged.
- Hard drive erased.
Types of Viruses
There are many types of computer viruses:- 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.
- Macro Virus : This is a new type of virus that use an application's own macro programming feature to distribute themselves. Unlike other viruses, macro viruses do not infect programs; they infect documents.
- Virus Hoax : Although there are thousands of viruses discovered each year, there are still some that only exist in the imaginations of the public and the press - known as virus hoaxes. These viruses hoaxes DO NOT EXIST, despite rumor of their creation and distribution.
Viruses/malware are commonly broken down into Classic Viruses, Trojans, Worms, adware, and spyware.
"Classic viruses" is a term coined in 1983. Classic viruses are malicious programs that rewrite existing computer code on your computer. Classic viruses are not so much unwanted additions to your system as they are mutations of existing code.
Trojans, or Trojan Horses, are additions to your system. These malicious programs masquerade as legitimate files in your email, deceiving you into willfully adding them to your hard drive. Trojans rely on you to intentionally open your computer to them. Once on your machine, Trojans then function as independent programs that operate secretly. Commonly, Trojans steal passwords or perform "denial of service" (overload your system) attacks. Examples of trojans include Backdoor and Nuker.
Worms, or Internet Worms, are also unwanted additions to your system. Worms are different from Trojans, though, because they copy themselves without your direct assistance... they robotically worm their way into your email, and begin broadcasting copies of themselves without permission. Because they do not require user intervention to reproduce, worms reproduce at an alarming rate. Examples of worms include Scalper, SoBig, and Swen.
Adware and Spyware are cousins to trojans, worms, and viruses. These programs "lurk" on your machine. Adware and spyware are designed to observe your Internet habits and then pummel you with advertising, or to report back to their owners via secret messages. Sometimes, these products will even use your hard drive to store and broadcast pornography and advertising back to the Internet. Nasty!
Whew, these semantics and definitions of viruses/malware can be very obscure to the non-technical user. However, it isn't crucial to distinguish between these products technically. What is important is how you consciously defend against these malware infections.
"Classic viruses" is a term coined in 1983. Classic viruses are malicious programs that rewrite existing computer code on your computer. Classic viruses are not so much unwanted additions to your system as they are mutations of existing code.
Trojans, or Trojan Horses, are additions to your system. These malicious programs masquerade as legitimate files in your email, deceiving you into willfully adding them to your hard drive. Trojans rely on you to intentionally open your computer to them. Once on your machine, Trojans then function as independent programs that operate secretly. Commonly, Trojans steal passwords or perform "denial of service" (overload your system) attacks. Examples of trojans include Backdoor and Nuker.
Worms, or Internet Worms, are also unwanted additions to your system. Worms are different from Trojans, though, because they copy themselves without your direct assistance... they robotically worm their way into your email, and begin broadcasting copies of themselves without permission. Because they do not require user intervention to reproduce, worms reproduce at an alarming rate. Examples of worms include Scalper, SoBig, and Swen.
Adware and Spyware are cousins to trojans, worms, and viruses. These programs "lurk" on your machine. Adware and spyware are designed to observe your Internet habits and then pummel you with advertising, or to report back to their owners via secret messages. Sometimes, these products will even use your hard drive to store and broadcast pornography and advertising back to the Internet. Nasty!
Whew, these semantics and definitions of viruses/malware can be very obscure to the non-technical user. However, it isn't crucial to distinguish between these products technically. What is important is how you consciously defend against these malware infections.
