Computer Virus

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Computer Virus
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Can you give some examples?
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What is a computer Virus?

• A computer virus
• is a small program
• created to do harm on computers
• it is running in the background, usually not
  known by the user.

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Typical Harmful Effects

• modify or destroy the data
• Creating garbage data in the hard disk
• Down-grade the performance of a computer system
• Producing irritating screen effect
• Introduce errors in output sending to printer

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Characteristics

• Hidden -- could not be known easily
• Replication -- will reproduce themselves to
  infect other systems

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Characteristics (2)

• Time bomb or logic bomb -- get activated at
  certain times or when some events happen

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Characteristics (3)

• Activated by execution -- i.e. if you do not run
  the virus, it could cause you no harm

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How virus spread?

• There are approximately 200 new viruses coming
  out each month

• Virus spread through
• floppy disks, CD-ROMs
• computer network
• illegal software
• Internet downloads
• email
• ...

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What virus may do? (payload)

• The payloads of a virus can be
• displaying annoying messages
• damaging the data stored in computers
• causing damage to a computer network
• damaging the hardware part of a computer (e.g.
  CIH)
• used to steal information in computers
• (any damage you can think of)

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Why are there viruses?

• What do you think?

Possibleanswers
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Types of computer virus

• Boot sector virus
• File virus
• Macro virus
• Worm
• Virus Hoax

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Boot sector virus

• Boot sector is the part of the disk where the
  computer will read when it starts up

boot sector
sectors
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Boot sector virus (2)

• If the virus hides itself inside the boot sector,
  it will be activated once the computer boots up

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File virus

• File virus hides itself at the beginning part of
  an executable file
• Every time the file is run, it gets activated

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Original program
Virus-infected program
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Macro virus

• MS Office products, e.g. Word, Excel, make use of
  macro (a subset of Visual Basic programming
  language) to help simplify operations
• Macro is very powerful and can access, or even
  delete files in a computer
• Macro viruses grow very fast in numbers with the
  popularity of MS Office products

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Macro Virus Demo
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Worm

• Virus designed to replicate itself to feed up a
  computers memory or a disk
• Performance of the computer will therefore be
  slowed down.
• During the duplication process, data or program
  in memory or disk is overwritten, thus causing
  data loss.

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Worm (2)

• Many worms are now spread through email
  attachments
• e.g. Happy99 was spread in the form of email
  attachments and would infect other computers
  though emailing itself to other users when it was
  run

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The latest worm - W32.Sasser.Worm

• It causes unpatched machines to start to reboot.
• System Affected Windows 2000, Windows XP
• With Sasser, users typically seem something like
  this

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Trojan Horse

• Have you heard of the story of Trojan Horse?

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Trojan Horse (2)

• Trojan horse pretends to do something while
  actually doing other things
• It comes as a useful program, e.g. beautiful
  screensaver -- and does something like deleting
  your files or passing your information to the
  outside world

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Discussion
Do you believe the following message?

"Don't read or open any e-mail title Good Times!
It will destroy your computer! Please forward
this letter to the others.
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File Attachment
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Virus hoax

• These are false virus warnings
• They appear in the form of chain-letters,
  asking you to forward the message to others
• Please delete these messages and do not forward
  to others!

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Virus hoax
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How to avoid virus?

• Do not participate in any BBS.
• Do not share diskette with the others
• Do not connect your computer to the network.
• Do not access the internet
• Do not switch on your computer

X
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How to protect yourself from computer virus?

• Install anti-virus software

Make sure you update the software frequently to
catch the new viruses
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How to protect yourself from computer virus? (2)

• Do not use illegal software
• Do not download unknown software
• Do not open emails (especially the attachments)
  from unknown senders

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How to protect yourself from computer virus? (3)

• Make backup copies of your important data

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Question

• A michaelangelo virus has been detected on your
  computer. You do not have the technical knowledge
  to remove it and no anti-virus program is
  available.What sensible precaution can be taken?