User:Sarswat2020

computer:- computer is an electronic device that can perform a variety of operation in accordance with a set of instructions called program. computer works upon binary language that is 0 or 1. There are some programming languages by which we can create software on computers. These programing languge is written in eiter in high lavel language or low level language. somthing about computer virus: What is a Computer VIRUS??

VIRUS stands for VITAL INFORMATION RESOURCE UNDER SEIZE.

Just as biological virus harms a human body ,computer virus are those who harm a computer system and effect the smooth working of the system.A program or piece of code that is loaded onto your computer without your knowledge and runs against your wishes. Viruses can also replicate themselves. All computer viruses are manmade. A simple virus that can make a copy of itself over and over again is relatively easy to produce. Even such a simple virus is dangerous because it will quickly use all available memory and bring the system to a halt. An even more dangerous type of virus is one capable of transmitting itself across networks and bypassing security systems

In computers, a virus is a program or programming code that replicates by being copied or initiating its copying to another program, computer boot sector or document. Viruses can be transmitted as attachments to an e-mail note or in a downloaded file, or be present on a diskette or CD. The immediate source of the e-mail note, downloaded file, or diskette you've received is usually unaware that it contains a virus. Some viruses wreak their effect as soon as their code is executed; other viruses lie dormant until circumstances cause their code to be executed by the computer. Some viruses are benign or playful in intent and effect ("Happy Birthday, Ludwig!") and some can be quite harmful, erasing data or causing your hard disk to require reformatting. A virus that replicates itself by resending itself as an email attachment or as part of a network message is known as a worm.

TYPES OF COMPUTER VIRUS

There are various types of VIRUS and are classified on how they effect your computer system:-

· Boot Virus

This type of virus affects the boot sector of a floppy or hard disk. This is a crucial part of a disk, in which information on the disk itself is stored together with a program that makes it possible to boot (start) the computer from the disk. The best way of avoiding boot viruses is to ensure that floppy disks are write-protected and never start your computer with an unknown floppy disk in the disk drive. Examples of boot viruses include: Polyboot.B, AntiEXE.

· Macro Virus

Macro viruses infect files that are created using certain applications or programs that contain macros. These mini-programs make it possible to automate series of operations so that they are performed as a single action, thereby saving the user from having to carry them out one by one. Examples of macro viruses: Relax, Melissa.A, Bablas, O97M/Y2K.

· File Infectors

This type of virus infects programs or executable files (files with an .EXE or .COM extension). When one of these programs is run, directly or indirectly, the virus is activated, producing the damaging effects it is programmed to carry out. The majority of existing viruses belong to this category, and can be classified depending on the actions that they carry out.

· Worms

A worm is a program very similar to a virus; it has the ability to selfreplicate, and can lead to negative effects on your system and most importantly they are detected and eliminated by antiviruses. Examples of worms include: PSWBugbear.B, Lovgate.F, Trile.C, Sobig.D, Mapson.

· Trojans or Trojan Horses

Another unsavory breed of malicious code are Trojans or Trojan horses, which unlike viruses do not reproduce by infecting other files, nor do they self-replicate like worms.

· Polymorphic virus

A polymorphic virus infects files with modified (usually encrypted) operational versions of itself, which it decrypts before executing. The virus and the decryption module are both modified on each execution, thus making it difficult to detect. The "Dark Avenger's Mutation Engine" (also known as MTE or DAME) has been released by virus writers to add this capability to any virus, but is now detectable by most antivirus tools.

· Metamorphic virus

A metamorphic virus rewrites itself completely each time it infects a new executable. This strategy requires the virus to include a metamorphic engine, making it large and complex, but also very difficult to detect. An example of a metamorphic virus is Win95.Zmist.A.

· Overwrite Viruses

Virus of this kind is characterized by the fact that it deletes the information contained in the files that it infects, rendering them partially or totally useless once they have been infected. The only way to clean a file infected by an overwrite virus is to delete the file completely, thus losing the original content. Examples of this virus include: Way, Trj.Reboot, Trivial.88.D.

· E-MAIL VIRUS

An e-mail virus is computer code sent to you as an e-mail note attachment which, if activated, will cause some unexpected and usually harmful effect, such as destroying certain files on your hard disk and causing the attachment to be remailed to everyone in your address book. Although not the only kind of computer virus, e-mail viruses are the best known and undoubtedly cause the greatest loss of time and money overall.

How does VIRUS affect a computer system?

 General Viruses

General computer viruses are packages of software that hide alongside other programs that seem valid. In most cases the virus is so small, and so well hidden, that by the time a user realizes it has "piggybacked" with his downloaded program, the virus has already started to cause its damage. Most general viruses act like human viruses. They do this by entering your system, and then taking advantage of it by using its components to duplicate itself and spread.

 Trojans

A trojan virus, sometimes referred to as a trojan horse, is named after its historical namesake. Just like the trojan horse in world history, a trojan disguises itself as something that it's not, but does not make itself known until it has made it onto your computer. Trojans can masquerade as games, programs or documents that you download online. Once you open the executable file, the trojan installs instead of the program and infects your computer. The trojan can then cause its damage, sometimes even erasing your hard disk. Unlike a general virus, a trojan is unable to duplicate itself automatically.

 Worms

A worm is an infection that exploits network connections. When a worm downloads itself onto your computer it uses network connections to other computers, as well as security holes to duplicate itself and spread. A worm uses one computer on a network system to scan all the other computers it is connected to for security holes. Once the worm finds a hole on another computer on the network, it copy and pastes itself into that computer by exploiting the security hole. It continues replicating until it runs out of computers to infect.

 Email Viruses

An email virus spreads as an attachment to an email. Sometimes this attachment can be seen, and other times it can't. Some email viruses can load onto your computer simply by opening an email into the preview frame. Once the virus has been opened, it automatically downloads its attachment to your computer. Some email viruses can also hijack your computer and send out copies of itself to everyone on your contacts list. Symptoms Of Virus Affected System

 Your computer always stops responding when you try to use Microsoft

Office products.

 You cannot start Windows Task Manager.

 Antivirus software indicates a virus is present.

 You received an e-mail message that has a strange attachment. When you open the attachment, dialog boxes appear or a sudden degradation in system performance occurs.

 There is a double extension on an attachment that you recently opened, such as .jpg.vbs or .gif.exe.

 An antivirus program is disabled for no reason and it cannot be restarted.

 An antivirus program cannot be installed on the computer or it will not run.

 Strange dialog boxes or message boxes appear on screen.

 Someone tells you that they have recently received e-mail messages from you containing attached files (especially with .exe, .bat, .scr , .vbs extensions),

which you did not send.

 New icons appear on the Desktop that you did not place there, or are not associated with any recently installed programs.

 Strange sounds or music plays from the speakers unexpectedly.

 A program disappears from the computer, and it was not intentionally uninstalled.

 A virus infection could also cause the following symptoms, but these symptoms could also be the result of ordinary Windows functions, or problems within Windows that is not caused by a virus.

 Windows will not start at all, even though you have not made any system changes, or you have not installed or removed any programs.

 Windows will not start because certain critical system files are missing, and then you receive an error message that lists those files.

 There is a lot of modem activity. If you have an external modem, you may notice the lights blinking extensively when the modem is not being used. You may be unknowingly supplying pirated software.

 The computer starts as expected sometimes, but at other times it stops responding before the desktop icons and taskbar appear.

 The computer runs very slowly and it takes a long time to start.

 Out-of-memory error messages appear, even though your computer has plenty of RAM.

 New programs do not install properly.

 Windows spontaneously restarts unexpectedly.

 Programs that used to run now stop responding frequently. If you try to remove and reinstall the software, the issue continues to occur.

 A disk utility such as Scandisk reports multiple serious disk errors.

 A partition completely disappears. PREVENTIVE MEASURES AGAINST

VIRUS

How a computer gets infected from virus? 1. From Infected Floppy Disk 2. From infected files downloaded from website. 3. From infected files from a infected CD 4. From infected E-mail attachment. 5. From running an unknown program or code on your computer.

What precautions or measures we can take to prevent virus from entering into our computer?

1. We should only use floppies that are from known source and are properly scanned from an anti-virus.

2. We can install a good firewall on our computer.

3. We can install good anti-spyware on our computer.

4. Never open an E-mail from an unknown person or unknown source.

5. Install a good Anti-Virus on your computer.

6. In the Internet Explorer go to go to Tools icon then go to the Internet Options.

What we should do when a virus attacks our computer?

1. First of all we should try to back-up our data that is most important to us.

2. If our computer is on network, just disconnect it from the network so that the virus should not spread in to the other computers.

3. Now run a good Anti Virus on the computer to scan for the viruses.

4. After the viruses are found by the anti-virus try to remove them with it.

5. Some times the viruses are internet Trojan horses or spyware, in that case you should use good anti-spyware to remove them.