In today’s technological arena, the most common botheration that we all face with our PCs, Laptops or Workstations is VIRUS. The problem is so vast and deep rooted that it becomes obvious for all to install effective antivirus software in our PC along with Internet Security, Malware or Trojan Remover with it.

In this article I would like to share some basic information about the computer viruses. I would like to classify it into 4 broad divisions which are as follows:

•What is a computer virus?
•What are the symptoms of computer virus?
•Types of  Virus
•What are the basic steps to get rid of the virus

• What is a computer virus?

The full form of computer virus is – Vital Information Resource under Siege. In terms of Computer Security, computer virus is a software program that, like a biological virus, makes copies of it and spreads from one computer to another computer and that interferes with computer operation.

The term "virus" was first used in this sense in print by Fred Cohen in his 1984 paper Experiments with Computer Viruses, where he credits Len Adleman with coining it. According to his definition, "a virus can spread throughout a computer system or network using the authorizations of every user using it to infect their programs. Every program that gets infected may also act as a virus and thus the infection grows." Using this definition it can be said that computer virus is an executable program code that may corrupt and/or delete program files, some specific data file (especially which contain executable code).

• What are the symptoms of computer virus?

The most common Symptoms that are seen when a computer is affected with a virus definition are:

•The computer restarts on its own in every few minutes.
•Programs that used to run stop responding frequently. Even if you remove and reinstall the programs, the issue continues to occur.
•Out-of-memory messages are received very frequently though there are sufficient spaces in RAM.
•An antivirus program cannot be installed on the computer, or the antivirus program is disabled without any valid reason.
•The infected file may create copies of itself and use up all the free spaces on hard disk.
•Slow internet connections.
•Distorted menus and dialogue box can be observed.
•You receive an e-mail message that has a strange attachment. If you open the attachment, dialog boxes appear, or a sudden degradation in system performance occurs.
•Receivers inform you that they have recently received e-mail messages from you that contained attached files though you did not send. The files that are attached to the e-mail messages have extensions such as .exe, .bat, .scr, and .vbs extensions.

If the above symptoms are being seen in a machine, the machine needs to be scanned with antivirus software thoroughly.

• Types Of Virus:

There are different types of computer viruses. Not all of them behave, replicate, or infect the same way. The following list will describe the most common types of computer viruses:

•Boot Virus: It affects the boot sector of a floppy disk or hard drive. Boot Sector is the most important area of a hard disk The best way to avoid these types of viruses is never start computer with an unknown floppy disk in the disk drive.

•Macro Virus: It stores as a macro to a document like MS Word or MS Excel or similar application. When user try to open that document the virus causes damage and also spread to other compatible document and applications so that any new document user going to create, will be infected.

•Rootkit Virus: Rootkit is a collection of programs that enables administer level access to a computer network. The term comes from the Linux administrator root user. This virus has an ability to rewrite the login script allowing it to accept the attacker's login regardless of any changes made to the system by administrators. They are too much effective in the distribution of illegal material over the internet because the rooted machine identifies itself as the source, instead of the attacker's machine.

•Polymorphic Virus: It is one of the most common viruses. Every time it changes its signature when replicates and affects a new file. This unique behavior makes them undetected by ordinary antivirus software.

•File Infectors: This virus infects the executable files like .EXE or .COM. When one of these programs is running, the virus is activated and does whatever it has been commanded to do. This virus typically resides in System Memory. One of the most common forms of it goes by the alias Win32.

•Trojan Horse: It is the most dangerous virus. Truly speaking, this is a very innocent looking virus that appears to perform some useful functions but secretly conducts some very harmful, destructive jobs like deleting a large number of data or allowing an outsider to gain an unauthorized access to the system. Trojan horse neither replicates nor copies itself but itself is a great threat towards system’s security. In many times it becomes so dangerous that a user has to format his OS to get rid of it.

Till now, we are talking about computer viruses and also discussing about its different types. But there are also other kinds of malwares which are not viruses by definition but do the same job as viruses do like destruction of important codes etc. We are now listing those malwares:

•Logic Bomb/Time Bomb: It is a dormant code that destroys junk data when certain conditions have been met. For example, an employee can write a code to delete a large number of files when his/her name will be removed from the project.

•Worms: A worm is a program that spreads copies of itself throughout a network or the internet without a host program. It creates problems by overloading the network as it replicates. Worms do damage by their presence rather than by performing a specific damaging act, as a virus does.

•Spyware: It is a technology to gather information about a person or organization without their knowledge or permission and relay those information’s to advertisers or other interested parties. Spyware can get in a computer as a software virus or as the result of installing a new program.

• What are the basic steps to get rid of the virus?

Though there is no particular way out to protect our PC from computer viruses but we can follow the steps written below to decrease the percentage of virus attack.

•Download and install good antivirus (AV) software and update the software regularly.
•Scan computer through that AV software and if any virus is detected, delete it immediately.
•If antivirus software cannot remove the virus and there is no removal tool available, your online search for the name of the virus may yield a set of instructions on how to manually remove the virus. But don’t follow those instructions blindly. Please be careful before starting the process.
•Don’t open any unknown file type attachment in your mail unless and until you are sure about that attachment.