These programs are classified into three categories:
- Trojan horses
- Logic bombs
- Malicious software programs that run within a web browser.
A virus-like program that pretends to do something else is called a Trojan horse. It appears as something interesting and harmless but when it runs it may have harmful effects.
A logic bomb infects a computers memory but does not replicate. It has the capability to erase a hard drive or delete some files. It is usually triggered by typing a combination of some keyboard keys or when some computer instructions are carried out. It can also be triggered when a certain date is reached.
Virus-like programs that run within a web browser are called malicious software. This often happens when a web browser appears in java applets and ActiveX Controls. These two usually increase a viral program to interfere with unprotected programs although they help the usefulness of a website.
History of Computer Viruses
Computer viruses date back to 1986 when the first virus (Brain Virus) appeared. This virus spread within one year and by 1987 it had spread to most parts of the world. The viruses grew more complicated in the late 1990s. These viruses spread by emails and even disabled the email servers around the world for some hours. The Love Bug and the I LOVE YOU viruses were the world’s most prevalent viruses when they stuck in year 2000.
They had infected 1 in every 5 computers worldwide. Other viruses that have been prevalent since 2003 include; Blaster worm which infected millions of PCs worldwide, SoBig which infected machines with an attempt to convert systems into networking relays which could send junk emails, and MyDoom virus which can spread faster than SoBig and can cause more damage.
