Types Of Computer Viruses





A computer virus is a program that is designed to damage your computer,
programs, and files. Like a virus in a living thing, a computer virus can spread if it is not
removed. Some viruses are more dangerous than others. One of the most common places
for a computer virus to appear is on a file found on the Internet or attached to an E-mail.
Computer viruses didn’t really exist until the mid 1980s. The first computer viruses were
created in university labs to demonstrate how much of a threat the vicious code could be.
There are many kind of viruses that exist today. Some of the most common of Computer
Viruses are: File Viruses, Boot Sector/Partition Viruses, Multi-Partite Viruses, Trojan
Horses, File Overwriters, Polymorphic viruses, and Stealth Viruses.
A File Virus is the most common kind of virus. These kinds of viruses usually
infect .EXE and COM files, which are the main component of a program or application.
A file virus can insert its own code into part of the file, so that when the infected program
file is run, the virus is executed first. Most file viruses are memory resident. Because of
this, they can easily attach themselves to other programs that are being run and start to
infect that file.

A simple virus will overwrite and destroy a host file, immediately letting
the user know that there is a problem because the software will not run. Because these
viruses are immediately sensed by the computer, they have a less chance to spread. More
complex written viruses will cause more damage, spread easier, and are harder to be
detected.
Boot sector viruses infect hard drives and floppy disks by putting itself on the
boot sector of the disk, which has the code that is run at boot up. Booting up from an
infected floppy, allows the virus to jump from the floppy to the hard drive. These viruses
are loaded first, and gain control of the system before MS-DOS could be loaded. Since
the virus is run before the operating system, it is not MS-DOS-specific and can infect any
PC operating system. These viruses stay in the RAM and infects every disk that is read by
the computer until the computer is rebooted. After reboot the virus is removed from
memory.
Multi-Partite Viruses are the worse of both file and boot sector viruses. They can
infect the host software components. These viruses spread like a file virus, but still insert
itself into a boot sector or partition table. Because of this, they are difficult to remove. An
example of this type of virus is the Tequila virus.
Trojan Horses are the worst kind of viruses that exist. They contain malicious
code that is meant to damage your computer. Unlike other viruses, this virus does not
replicate itself. This virus waits until the trigger event. When the trigger event occurs, a
message is displayed or files are damaged.
File Overwriters are viruses that link themselves to a program, leaving the original
code intact and adding themselves over and over to as many files as possible. These
viruses are made simply to keep copying itself. While, this virus is copying itself it is
taking up more disk space and slowing down performance. Since these viruses often have
flaws in them, they can inadvertently damage or destroy data. The worst kind of file
overwriters, wait until the trigger event, then start to destroy files.
Most of the viruses that exist today are Polymorphic. Like the human AIDS virus,
polymorphic viruses grow fast to escape detection by anti-virus programs. Special
encrypted code within this virus allows the virus to hide from detection. There are a
limited number of kinds of polymorphic viruses. Because of this, they are easier to notice.
An example of this would be the Whale Virus , which has 32 different forms. Stealth
viruses are similar to a stealth aircraft. Like a stealth aircraft, they make themselves
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invisible to be detected. The virus hides itself into the file and makes it look like the
program is running normal. This is a memory-resident virus.(…)
It is dangerous when making predictions about the future. Unless you can see into
the future, it is not wise to try to see what would happen. Because of this, someone can
make a broad judgment of future virus development.

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