Computer viruses

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In defining computer viruses Parsons and Oja wrote that the technical definition of a computer virus is a set of program instructions that attaches itself, and spreads to other files. Viruses corrupt files, destroy data, displays irritating messages, or otherwise disrupt computer operations. (185)

In continuing, Parsons and Oja explained that there is a common misconception that viruses contain program codes to spread themselves from one computer to another. They do not. The reason viruses spread is because people redistribute infected files by exchanging disks and compact discs, sending e-mail attachments and downloading software from the Web. (185)

For the book titled Computer Concepts, it is learned that a computer virus generally infects the files executed by your computer such as those with .exe, .com or .vbs extensions. When a computer executes an infected program, it also executes the attached virus instructions. These instructions then remain in the Random Access Memory, waiting to infect the next program that the computer runs or the next disc it accesses. (185)

In addition to replicating itself, a virus might perform a trigger event, sometimes referred to as payload. The resulting effects can range from displaying an annoying message to corruption of data on the computer's hard disk. Trigger events are often keyed to a specific date. The Michelangelo virus, for example was designed to damage hard disks on March 6, the birthday of artist Michelangelo. (185)

A key characteristic of viruses is their ability to lurk in a computer for days or months, quietly replicating themselves. While this is taking place, a user might not even know that his or her computer has a virus; therefore it is easy to inadvertently spread infected files to other people's computers. (185)

According to CNN.com Technology, there are thousands of variations of viruses, most falls into one of the following six general categories, each of which works its magic slightly differently.

The first category of viruses is the Boot Sector Virus. This virus replaces or implants itself in the boot sector---an area of the hard drive (or any other disk) accessed when you first turn on your computer. This kind of virus can prevent you from being able to boot your hard disk. Second is the File Virus which infects applications. These executables then spread the virus by infecting associated documents and other applications whenever they're opened or run. Third is the Macro Virus. It is written using a simplified macro programming language, these viruses affect Microsoft Office applications, such as Word and Excel, and account for about 75 percent of viruses found in the wild. A document infected with a macro virus generally modifies a pre-existing, commonly used command (such as Save) to trigger its payload upon execution of that command. Fourth is the Multipartite Virus. He virus infects both files and the boot sector--a double whammy that can reinfect your system dozens of times before it's caught. Fifth is the Polymorphic Virus which changes code whenever it passes to another machine. In theory these viruses should be more difficult for antivirus scanners to detect, but in practice they're usually not that well written. Finally there is the Stealth Virus which hides its presence by making an infected file not appear infected.

It must be noted that not all malicious codes are viruses. A common misconception is that other kinds of electronic nasties, such as worms and Trojan horse applications, are viruses. They aren't. Worms, Trojan horses, and viruses are in a broader category analysts call "malicious code." A worm program replicates itself and slithers through network connections to infect any machine on the network and replicate within it, eating up storage space and slowing down the computer. But worms don't alter or delete files. A Trojan horse doesn't replicate itself, but it is a malicious program disguised as something benign such as a screen saver. When loaded onto your machine, a Trojan horse can capture information from your system -- such as user names and passwords--or could allow a malicious hacker to remotely control your computer.

Daily many computer users participate in the spreading of viruses without knowing they did. Viruses can slip into your computer from a variety of sources. The most common sources of file viruses, boot sector viruses, and Trojan horses are floppy disks, homemade compact discs, and Web sites that contain games and other supposedly fun stuff.
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A common misconception is that write-protecting your floppy discs by opening a small hole in the corner of the disc prevent virus infection. Although a virus cannot jump onto your disk when it is write-protected, you must remove the write protection each time you save a file on the disk. With the write-protection removed, your disk is open to a virus attack.

Another common source of viruses is e-mail attachments. A seemingly innocent attachment could harbour a file virus or boot sector virus. Typically, infected attachments look like executable files, usually with .exe filename extensions, although they ...

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