What is Computer Virus and What are its Types?

Computer virus is a small block of coded instruction that obtains control of a PC’s CPU and directs it to perform unusual and often destructive actions.

Virus also called perverse software is a program which knows how to copy itself and attaches itself to other programs which further spread the infection. Antivirus is the method to get rid of perverse software or the viruses.

Computer Infected by a Virus Attack

Types of Computer Virus

Viruses are classified in the following types:

  • Trojan Horse
  • Time and. Logic Bombs
  • Melissa and Ska Virus pertaining to various MS Office files

1. Trojan Horse

A Trojan Horse is a program that invades a computer system by secretly attaching itself to a valid program downloaded into the computer. It may be used to locate password information, or it may alter an existing program to make it easier to gain access to it.

A virus is called a Trojan horse that continues to infect pro­grams over and over again. It also pretends to do something use­ful or interesting. But when run, it produces some harmful effects like scrambling FAT (File Allocation Table) or formatting the hard disk.

2. Time and Logic Bombs

A Time and Logic bomb is a program that destroys data. For example, it may reformat the hard disk or randomly insert gar­bage into data files. A time bomb as the name suggests, is trig­gered by an event. It can format the hard disk on a given date or slow down computer every Friday or make a ball bounce around the screen.

A logic bomb may be brought into a personal computer by downloading a public-domain program that has been tampered with.

Once executed, the logic bomb usually does its damage right away, whereas a software virus slowly invades a system and attaches itself to oilier programs too

3. Melissa and SKA Viruses

Melissa virus attacks MS Word documents and spreads very fast. This virus affects Word documents by installing itself to Nor­mal.doc and disabling the macro protection message and infects all the Word files opened or created subsequently. The message generated by the virus says “Here is a document you asked for …don’t show anyone else”.

A new virus called Melissa spread around the world rapidly, infecting many computers and bringing down networks. It was a Word Macro virus and used Outlook to send infected documents across the Internet.

When an infected document is opened in Office 2000, it set several registry keys and then proceeds to execute the most dan­gerous part of the code. Using Outlook, the virus finds the first 50 entries from the user’s Address Book and sends the infected document as an attachment to those selected recipients.

The sub­ject line in all the sent messages read, “Important Message from—UserName.” This virus brought many companies and the Internet users to their knees. Mail servers around the world were bogged down handling the sudden influx and explosion of mes­sages.

Melissa has two types of impact. First the initial snowball effect and then the ripple effect. If the end users open the attachment that causes the problems, corporate systems are flooded with resource-hogging e-mails, in exponentially increasing numbers. As the snowball gets momentum, more e-mail servers are affected.

The role of the e-mail server has changed over the years. It has evolved from the electronic equivalent of a post office (storing and forwarding text messages) to a facilitator of group collaboration and offline database transactions.

In terms of their “groupware” aspects, these servers have grown to support other group collabo­rations and communications around topics.

Companies that depend on teams of people, who in turn depend on the collaboration services provided by these servers, felt the pinch more than those companies that were less team-and technology-dependent.

There virus called Ska increases the size of the file and changes the extension of the files to .ska.

These viruses delete the MS Office Document files or change their contents. Happygg also known as Ska or I-Worm is a computer Worm for Windows.

Buy Anti Virus Software for your Pc/Laptop:

How do Computer Virus Spread?

Viruses spread through pen drives, e-mails, Internet downloads and other networks. They may remain dormant and strike when the infected programme or file is used.

One can detect the pres­ence of a virus by strange messages which may pop up on the screen. There may be unusual changes in the size of programs, strange file names in the contents, reduction on free space in the memory and prolonged disk activity or drives working on their own.

If you do not identify these glitches, viruses go undetected and get enough time to activated and spread out.

Virus Scanners are useful in detecting such viruses.


Also Read:

An aspiring BCA student formed an obsession with Computer/IT education, Graphic Designing, Fitness, YouTube and Blogging, and Helping Beginners to learn these skills and implement them in their life.

Share the Post:

Leave a Comment