Viruses, Trojans and Worms

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Viruses, Trojans and Worms

• MIS
• By William Brooks

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Computer Viruses

What is a Computer Virus? To be defined as a
virus, a program must

• Replicate itself in order to carry out a mission.
  
• Be dependent on a "host" to carry out the
  mission.
• Create damage to the computer system "infected".

Simple Definition A virus is a program which
reproduces itself , hides in other computer
code without permission and does nasty things to
software and hardware. The program code that
causes unwanted activity is called the payload.

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Virus Effects

• Slows your system down and makes it inactive to
  do even minor task.
• Trivial, simply reproduces or displays messages.
• Minor, alters or deletes infected files.
• Moderate, wipes out entire disk drive.
• Major, slowly corrupts data with pattern, making
  restoration difficult.
• Severe, slowly corrupts data without pattern,
  making restoration impossible.
• Unlimited, virus which discovers system
  administrator's password and mails it to one or
  more users, tempting them to use it for illegal
  purposes.

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Virus Types

• Viruses are classified by the portion of the
  system they affect.
• Boot Viruses
• Infect the boot block on a floppy or hard disk.
• Usually replaces the boot block with all or part
  of a virus program.
• Most have trigger dates, when booted on that day
  severe damage will be done.
• Virus loads into memory and infects other disks.
• File Viruses
• Infect .EXE or .COM files.
• Usually append the virus code to the file, new
  versions hide the virus.
• Damage is done when program is run and the virus
  will attach to other files.
• Trojans
• Computer Trojans are simply malicious computer
  programs disguised as something useful. The major
  difference between viruses and Trojans is that
  viruses reproduce, while a Trojan is just a one
  time program which executes its payload as soon
  as the Trojan is executed. Trojans are the most
  common way of bringing a virus into a system.

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Virus Types (continued)
Worms Computer Worms are reproducing programs
that run independently and travel across network
connections. The main difference between viruses
and worms is the method in which they reproduce
and spread. A virus is dependant upon a host file
or boot sector, and the transfer of files between
machines to spread, while a worm can run
completely independently and spread of its own
will through network connections.
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Virus Prevention

• Use an antivirus software program.
• Check for virus protection updates on a weekly
  basis, and system scan.
• Use a Firewall to help protect your files and
  data.
• Keep your operating system/software application
  up to date by installing updates/patches from the
  vender
• Only install software from respectable Vender.
• Do not download from programs or files from
  unknown websites.
• Do not open attachments in emails unless you scan
  it with antivirus protection first.

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References
The Textbook Using MIS And http//ksi.cpsc.uca
lgary.ca/courses/547-96/cochrane/present/index.htm
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