Definition of Computer viruses and its types.

A computer virus is a program or a set of programs that disrupts the normal functioning of a computer. A virus infects or destroys data. It enters into a computer without the permission or knowledge of the users.  The full form of VIRUS is Vital Information Resources Under Seize. The essential resources of a computer, like memory, processing speed, data, and programs are hampered when virus spreads into the system.

Virus programs are self-replicating programs while continuously expand their reach by infecting more and more computer files, resulting in loss of speed and destruction of data. Almost all viruses are attached to an executable file, which means that if a virus exists on a computer, it will not infect the computer unless we run or open the malicious program.

                            

Many times while working on a computer, it gets hanged, restart frequently, and sometimes data gets lost. Generally we call it a virus attack. However in reality, it is not only the virus that does it all, but worms, trojans,spyware, etc are equally responsible for improper functioning of a computer. A common blunder which makes people while discussing about computer virus is to refer a computer worms or Trojans as a virus. 

While the words Trojan, worms, virus, are not exactly same. These are all malicious programs that can cause damage to a computer , but there are some difference between the three. Let us see about these differences and help us to protect our computers from their damaging effects.

Types of virus

Virus can be classified into two major categories :-

Boot viruses:-  These  viruses infect the boot record or master boot records. They  change the location of the boot record that is responsible for loading the operating system in memory by copying it. Boot virus becomes active at that time of booting the machine. Example are- disk killer, stone virus etc.

Program file viruses:-  These  viruses infect executable files or programs such as those with extension, like .com, .exe, .ovl, .drv, .sys, etc. these program get loaded in the memory during execution. The virus becomes active in memory by replicating itself and infecting files on the disk. Sunday, cascade, etc. are the examples of program file virus.


Virus symptoms

·         A virus cause many problems in a computer, such as:-

·         Decreasing the speed of a  computer by decreasing the memory..

·         Causing strange movements or patterns on the screen.

·         Frequently hanging of the system.

·         Displaying unusual message like “your PC is stoned”.

·         Increasing the use of disk space and causing growth in file size  as the virus attaches itself many files.

·         Showing abnormal write protect error.

·         Deleting or damaging files.

·         Reformatting the hard disk.

·         Displaying a change in the data against the filename in the directory, when a virus modifies the file.

Steps to prevent virus

·         Every PC should equipped  with some antivirus program.

·         Always scan the Pendrive before copying files.

·         Do not install pirated software.

·         Scan the hard disk twice a month.

·         Take the backup of important files everyday.


Computer worms

A worms is similar to virus in design and is considered to be a sub-class of a virus. A worm spreads from computer to computer, but unlike a virus, it has the capacity to travel without any human action. The biggest danger with the worm is its capability to replicate itself on a system. Hence, rather than your computer sending out a single worm, it could send out hundreds or thousands of copy itself, creating huge devastating effect. Due to the copying nature of worm and it  capability to travel across networks, the end result in most case is heavy consumption of system memory causing web server, network server and individual computers to stop responding.


TROJANS

A Trojan Horse, at first glance will appear to be a useful software but will actually damage the computer once it is installed.  Users on the receiving end of a Trojan horse are usually ticked into opening then because they appears to be receiving useful software of files from a genuine source. When a Trojan is activated on a computer, the results can vary. Some Trojans are design to be more irritating than malicious, like changing your desktop, adding silly active desktop icon or they can cause serious damage by deleting files and destroying information from the system. Unlike viruses and worms, Trojans do not reproduce by infecting other files nor do they self-replicate.

Trojans come in two parts, client part and a server part. The server part is installed on the victim’s machine and client part is on the attacker’s machine. Server part of the Trojans of an executable files called as server.exe. this  executable file is hidden behind any normal file like song or image. When the victims unknowingly runs this file, a part on victim’s computer gets opened and the attackers gets hold of his PC through the control panel.

MALWARE

The term Malware is made up of two words, malicious and software. Ii is a software that enters into a computer and damages it without the user’s knowledge. Malwares are trouble causing problems. It may be a virus, worm, Trojan horse, or spyware. Malwares not only interrupt the normal working of a computer but also steal important information. Some examples of data stealing malwares are:

BANCOS: It is an information stealer that waits for a user to access banking websites, and while surfing, it steals the sensitive information.

GATOR: It secretly monitors web-surfing habits and sends this information to its server, which then throws related pop-up advertisements

SPYWARE

Spyware is a type of malware that is installed on computers and collects information about users without their knowledge. Spyware programs secretly monitor the user’s computing. They can collect various types of personal information, such as internet surfing habits, visited web page, and transmit this information in the background to someone else. They can also interfere with user’s control of the computer in other ways, such as installing additional software and redirecting the web browser activity to other pages. Sometimes they also change the computer setting into results in slow connection speed, and wrong functionality of other program. Spyware can also gather information about e-mail address, passwords and even credit card numbers

SPAM

Spam mails are unwanted bulk e-mails that come strange sources. These are generally sent in large number for commercial advertising. In spamming, millions of copies of the same message are sent to e-mail users worldwide. Spam is serious security concern as it can be used to deliver Trojan Horses, viruses, worms, spyware, and organize targeted phishing attacks.

ANTIVIRUS SOFTWARE

Antivirus software are computer programs that are designed to identify, prevent, and remove viruses from a computer. They perform the following tasks into a computer:

    Scan the computer files to look for known viruses from the virus dictionary.

    Identify suspicious behavior from any computer program that might indicate infection.

   Scan the incoming e-mails which might contain virus in the attachment.

   Simply installing an antivirus software in our computer does not guarantee the 100% protection, as the Installed antivirus program would not be able to detect any new virus programs. We should update our computer with the latest version of antivirus definition. Most of the antivirus software companies provide the facility to download the latest updates from their websites.

Some popular antivirus software in use nowadays are as follows:

·         Mcafee

·         AVG Antivirus

·         Microsoft Security Essential

·         Symantec Norton Antivirus

·         Quick Heal