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Types, effects and symptoms of computer virus


Date Posted: 3/19/2018 2:59:06 PM

Posted By: Bom  Membership Level: Bronze  Total Points: 57


A computer virus is a program that has the ability to reproduce/replicate itself without the user’s knowledge. For example, it may attach itself to the DOS program FORMAT and run every time you format a diskette.
There are other types of software that can cause problems in a PC. However, no other software can replicate and it is this characteristic that makes a program a virus.

Effects of Viruses:
-A virus can destroy/delete or corrupt data e.g. those on specific applications such as all Excel files or all word files e.g. Sircam worm deletes data.

-Display irritating message, or otherwise disrupt computer operations. Most viruses stay in your PC’s memory where they can cause problems by interfering with other software you are trying to run.

-Disable hardware, making the computer unusable.

-It can perform dangerous operations like formatting the hard disk.

-It consumes the disk space, memory and wastes the processor time.

Once you have a virus, it is very likely that you will pass it on to a colleague or a customer, who may well lose confidence in you and your company.

Types of Viruses:

1: File viruses: - file virus infects the executable program files on your computer system. These usually, but not always, have COM or EXE file extensions. When you run an infected program, your computer also runs the attached virus instructions to replicate or to deliver its payload. The term payload refers to the ultimate mission of a virus. For example, the payload of the “stoned” virus is the message,” your Pc is now stoned”.

Only a few viruses such as Cinderella and Frodo, are designed to infect data files. Because a virus needs to be executed to spread, a data file can only be a carrier,

it cannot deliver the payload.

2: Boot Sector Viruses -these infect the system files your computer uses every time you turn it on. The boot sector is the part of every hard disk and diskette, which is read by the computer every time you start it up. The partition sector, also called the Master Boot Record (MBR), is the first part of the hard disk to be read after the system has started up. It contains information such as the number of sectors in each partition and the location of all the partitions.

If your booting disk is infected and you try to boot your computer with it then the following message is likely to be displayed.

Non-system disk or disk error
Replace and press any key when ready.

By this time the virus has already run and your PC may already be infected. In most cases, the virus loads itself into memory and infects the partition sector of the hard disk. It replaces the original partition sector with its own code. If this partition sector is infected, when the PC is rebooted from the hard disk, the virus is loaded into memory. Any diskette subsequently accessed is infected.

3:Companion Viruses -if you have a COM file and an EXE file of the same name, Dos always runs the COM file in preference to the EXE file is not file extension is given. Companion viruses make use of this fact by creating COM files with the same name as the legitimate EXE files, thus ensuring they are executed. They then pass control to the original EXE file which runs normally.

Symptoms of the Viruses

The symptoms of a virus infection depend on the virus. The following symptoms might indicate that your computer has contracted a virus.

>Your computer displays annoying messages such as “Gotcha! Arf Arf! “You are stoned”
>Your computer develops unusual visual or sound effects. For example, characters begin to disappear from your screen or the sound of a flushing toilet comes for your computer’s speakers.
>You have difficulty saving files.
>Your computer suddenly seems to work very slowly.
>Files are mysteriously missing.
>Your computer reboots unexpectedly.
>Your executable files unaccountably increases in size.

Viruses are just one type of program in a large category of software designed by hackers to disrupt or damage the data on computers.

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