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In addition to genuine viruses, there are those dire email warnings about disk-eating attachments that sometimes land in your inbox. Next time you receive a well-meaning virus warning, check a virus hoax list before you pass the message on to all your friends.

Please ignore any messages regarding these supposed "viruses" and do not pass them on. Passing on these hoax messages only serves to further propagate them. "New" virus hoaxes are more often than not, merely recycled old hoaxes, with the addition of a few minor differences. As such it is possible to spot the tell-tale signs of a hoax. Typical phrases in a virus hoax might be:
Do not open! Doing so will result in the deletion of all of the files on your hard drive! Forward this message to all your friends!

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What is a virus? A computer virus is a small programme written to alter the way a computer operates, without the permission or knowledge of the user. A virus must meet two criteria:
  • It must execute itself. It will often place its own code in the path of execution of another programme.
  • It must replicate itself. For example, it may replace other executable files with a copy of the virus infected file. Viruses can infect desktop computers and network servers alike.
Some viruses are programmed to damage the computer by damaging programmes, deleting files, or reformatting the hard disk. Others are not designed to do any damage, but simply to replicate themselves and make their presence known by presenting text, video, and audio messages. Even these benign viruses can create problems for the computer user. They typically take up computer memory used by legitimate programmes. As a result, they often cause erratic behavior and can result in system crashes. In addition, many viruses are bug-ridden, and these bugs may lead to system crashes and data loss.

There a five recognized types of viruses:
  • File infector viruses : File infector viruses infect programme files. These viruses normally infect executable code, such as .com and .exe files. The can infect other files when an infected programme is run from floppy, hard drive, or from the network. Many of these viruses are memory resident. After memory becomes infected, any noninfected executable that runs becomes infected. Examples of known file infector viruses include Jerusalem and Cascade.
  • Boot sector viruses : Boot sector viruses infect the system area of a disk--that is, the boot record on floppy disks and hard disks. All floppy disks and hard disks (including disks containing only data) contain a small programme in the boot record that is run when the computer starts up. Boot sector viruses attach themselves to this part of the disk and activate when the user attempts to start up from the infected disk. These viruses are always memory resident in nature. Most were written for DOS, but, all PCs, regardless of the operating system, are potential targets of this type of virus. All that is required to become infected is to attempt to start up your computer with an infected floppy disk Thereafter, while the virus remains in memory, all floppy disks that are not write protected will become infected when the floppy disk is accessed. Examples of boot sector viruses are Form, Disk Killer, Michelangelo, and Stoned.
  • Master boot record viruses : Master boot record viruses are memory resident viruses that infect disks in the same manner as boot sector viruses. The difference between these two virus types is where the viral code is located. Master boot record infectors normally save a legitimate copy of the master boot record in an different location. Windows NT computers that become infected by either boot sector viruses or master boot sector viruses will not boot. This is due to the difference in how the operating system accesses its boot information, as compared to Windows 95/98. If your Windows NT systems is formatted with FAT partitions you can usually remove the virus by booting to DOS and using antivirus software. If the boot partition is NTFS, the system must be recovered by using the three Windows NT Setup disks. Examples of master boot record infectors are NYB, AntiExe, and Unashamed.
  • Multi-partite viruses : Multi-partite (also known as polypartite) viruses infect both boot records and programme files. These are particularly difficult to repair. If the boot area is cleaned, but the files are not, the boot area will be reinfected. The same holds true for cleaning infected files. If the virus is not removed from the boot area, any files that you have cleaned will be reinfected. Examples of multi-partite viruses include One_Half, Emperor, Anthrax and Tequilla.
  • Macro viruses : These types of viruses infect data files. They are the most common and have cost corporations the most money and time trying to repair. With the advent of Visual Basic in Microsoft's Office 97, a macro virus can be written that not only infects data files, but also can infect other files as well. Macro viruses infect Microsoft Office Word, Excel, PowerPoint and Access files. Newer strains are now turning up in other programmes as well. All of these viruses use another programme's internal programming language, which was created to allow users to automate certain tasks within that programme. Because of the ease with which these viruses can be created, there are now thousands of them in circulation. Examples of macro viruses include W97M.Melissa, WM.NiceDay and W97M.Groov.


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