Which is the example of computer virus?

Answer 1

Virus (computer), a self-duplicating computer program that spreads from computer to computer, interfering with data and software. Just as biological viruses infect people, spreading from person to person, computer viruses infect personal computers (PCs) and servers, the computers that control access to a network of computers. Some viruses are mere annoyances, but others can do serious damage. Viruses can delete or change files, steal important information, load and run unwanted applications, send documents via electronic mail (e-mail), or even cripple a machine's operating system (OS), the basic software that runs the computer.

How infection occurs?

A virus can infect a computer in a number of ways. It can arrive on a floppy disk or inside an e-mail message. It can piggyback on files downloaded from the World Wide Web or from an Internet service used to share music and movies. Or it can exploit flaws in the way computers exchange data over a network. So-called blended-threat viruses spread via multiple methods at the same time. Some blended-threat viruses, for instance, spread via e-mail but also propagate by exploiting flaws in an operating system.

Traditionally, even if a virus found its way onto a computer, it could not actually infect the machine-or propagate to other machines-unless the user was somehow fooled into executing the virus by opening it and running it just as one would run a legitimate program. But a new breed of computer virus can infect machines and spread to others entirely on its own. Simply by connecting a computer to a network, the computer owner runs the risk of infection. Because the Internet connects computers around the world, viruses can spread from one end of the globe to the other in a matter of minutes.

Types of viruses

There are many categories of viruses, including parasitic or file viruses, bootstrap-sector, multipartite, macro, and script viruses. Then there are so-called computer worms, which have become particularly prevalent. A computer worm is a type of virus. However, instead of infecting files or operating systems, a worm replicates from computer to computer by spreading entire copies of itself. Parasitic or file viruses infect executable files or programs in the computer. These files are often identified by the extension .exe in the name of the computer file. File viruses leave the contents of the host program unchanged but attach to the host in such a way that the virus code is run first. These viruses can be either direct-action or resident. A direct-action virus selects one or more programs to infect each time it is executed. A resident virus hides in the computer's memory and infects a particular program when that program is executed. Bootstrap-sector viruses reside on the first portion of the hard disk or floppy disk, known as the boot sector. These viruses replace either the programs that store information about the disk's contents or the programs that start the computer. Typically, these viruses spread by means of the physical exchange of floppy disks. Multipartite viruses combine the abilities of the parasitic and the bootstrap-sector viruses, and so are able to infect either files or boot sectors. These types of viruses can spread if a computer user boots from an infected diskette or accesses infected files. Other viruses infect programs that contain powerful macro languages (programming languages that let the user create new features and utilities). These viruses, called macro viruses, are written in macro languages and automatically execute when the legitimate program is opened. Script viruses are written in script programming languages, such as VBScript (Visual Basic Script) and JavaScript. These script languages can be seen as a special kind of macro language and are even more powerful because most are closely related to the operating system environment. The 'ILOVEYOU' virus, which appeared in 2000 and infected an estimated 1 in 5 personal computers, is a famous example of a script virus. Strictly speaking, a computer virus is always a program that attaches itself to some other program. But computer virus has become a blanket term that also refers to computer worms. A worm operates entirely on its own, without ever attaching itself to another program. Typically, a worm spreads over e-mail and through other ways that computers exchange information over a network. In this way, a worm not only wreaks havoc on machines, but also clogs network connections and slows network traffic, so that it takes an excessively long time to load a Web page or send an e-mail.

Protection against viruses

Computer users can prepare for a viral infection by creating backups of legitimate original software and data files regularly so that the computer system can be restored if necessary. Viral infection can be prevented by obtaining software from legitimate sources or by using a quarantined computer-that is, a computer not connected to any network-to test new software. Plus, users should regularly install operating system (OS) patches, software updates that mend the sort of flaws, or holes, in the OS often exploited by viruses. Patches can be downloaded from the Web site of the operating system's developer. However, the best prevention may be the installation of current and well-designed antiviral software. Such software can prevent a viral infection and thereby help stop its spread.

Several types of antiviral software can be used to detect the presence of a virus. Scanning software can recognize the characteristics of a virus's computer code and look for these characteristics in the computer's files. Because new viruses must be analyzed as they appear, scanning software must be updated periodically to be effective. Other scanners search for common features of viral programs and are usually less reliable. Most antiviral software uses both on-demand and on-access scanners. On-demand scanners are launched only when the user activates them. On-access scanners, on the other hand, are constantly monitoring the computer for viruses but are always in the background and are not visible to the user. The on-access scanners are seen as the proactive part of an antivirus package and the on-demand scanners are seen as reactive. On-demand scanners usually detect a virus only after the infection has occurred and that is why they are considered reactive.

Antivirus software is usually sold as packages containing many different software programs that are independent of one another and perform different functions. When installed or packaged together, antiviral packages provide complete protection against viruses. Within most antiviral packages, several methods are used to detect viruses. Checksumming, for example, uses mathematical calculations to compare the state of executable programs before and after they are run. If the checksum has not changed, then the system is uninfected. Checksumming software can detect an infection only after it has occurred, however. As this technology is dated and some viruses can evade it, checksumming is rarely used today.

Most antivirus packages also use heuristics (problem-solving by trial and error) to detect new viruses. This technology observes a program's behavior and evaluates how closely it resembles a virus. It relies on experience with previous viruses to predict the likelihood that a suspicious file is an as-yet unidentified or unclassified new virus.

Other types of antiviral software include monitoring software and integrity-shell software. Monitoring software is different from scanning software. It detects illegal or potentially damaging viral activities such as overwriting computer files or reformatting the computer's hard drive. Integrity-shell software establishes layers through which any command to run a program must pass. Checksumming is performed automatically within the integrity shell, and infected programs, if detected, are not allowed to run.

Once a viral infection has been detected, it can be contained by immediately isolating computers on networks, halting the exchange of files, and using only write-protected disks. In order for a computer system to recover from a viral infection, the virus must first be eliminated. Some antivirus software attempts to remove detected viruses, but sometimes with unsatisfactory results. More reliable results are obtained by turning off the infected computer; restarting it from a write-protected floppy disk; deleting infected files and replacing them with legitimate files from backup disks; and erasing any viruses on the boot sector.

Answer 2

A computer virus is a file that will corrupt your computer files and cause it to malfunction or not work at all. Files can be lost and destroyed by a computer virus. An antivirus is software that monitors your computer and scans files to ensure that they do not get infected by viruses.

Answer 3

The I love you, Blaster worm and rouge anti-spyware sites are good examples.

Answer 4

examples: gonnhorea, aids, hiv, crabs, the clap, and siflis

Answer 5

Some examples of Computer Viruses are: Conficker, ILOVEYOU, MS Antivirus.