Introduction to Computer Viruses and How to Protect Yourself

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Introduction to Computer Viruses and How to
Protect Yourself

• Jason Gratto
• Emily Love
• Lyndsey Blakeley

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What is a Computer Virus?

• A computer virus is a small software program that
  can copy itself and infect a computer without
  permission or knowledge of the user.
• The virus code will be executed when the infected
  program is executed.
• Computer viruses are called viruses because they
  share some of the traits of biological viruses. A
  computer virus passes from computer to computer
  like a biological virus passes from person to
  person. A computer virus must piggyback on top of
  some other program or document in order to get
  executed.
• .

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What do they do?

• Viruses are programmed to damage programs, delete
  files, reformat the hard disk or simply replicate
  themselves and make their presence known by
  presenting text, video, or audio messages. These
  viruses take up computer memory used by
  legitimate programs. As a result, they often
  cause erratic behavior and can result in system
  crashes.
• Viruses have the potential to infect any type of
  executable code, so are able to infect code in
  floppy disks or hard drives. They can infect word
  processing and spreadsheet documents that use
  macros, and HTML documents containing JavaScript
  can also spread viruses.

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What computer viruses are not!

• Viruses are a type of malicious software, but
  malware also includes many other types of
  problematic program codes, so they are not
  synonymous!
• Viruses are sometimes confused with computer
  worms and Trojan horses. A worm can spread itself
  to other computers without needing to be
  transferred as part of a host, and a Trojan horse
  is a file that appears harmless. Both worms and
  Trojans will cause harm to computers when
  executed, but they are not viruses.

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Types of computer viruses

• Resident Viruses Permanent and dwells in the
  RAM memory. It can overcome and interrupt all of
  the operations executed by the system.
• Direct Action Viruses - Replicates and takes
  action when it is executed. It will infect files
  in the directory or folder that it is in.
• Overwrite Viruses - Deletes the information
  contained in the files that it infects, rendering
  them useless. The only way to clean a file
  infected by an overwrite virus is to delete the
  file completely, thus losing the original
  content.
• Boot Virus - Affects the boot sector of a floppy
  or hard disk. The best way of avoiding boot
  viruses is to ensure that floppy disks are
  write-protected and never start your computer
  with an unknown floppy disk in the disk drive.
• Macro Virus - Infect files that are created using
  certain applications or programs that contain
  macros.
• Directory Virus - Change the paths that indicate
  the location of a file, so you are unknowingly
  running the virus program, while the original
  file and program have been previously moved by
  the virus. Once infected it becomes impossible to
  locate the original files.

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More types of computer viruses

• Polymorphic Virus - Encode themselves in a
  different way every time they infect a system.
  This makes it impossible for anti-viruses to find
  them using string or signature searches (because
  they are different in each encryption) and also
  enables them to create a large number of copies
  of themselves.
• File Infectors - Infects programs or executable
  files so that when one of these programs is run
  the virus is activated, producing the damaging
  effects it is programmed to carry out.
• Companion Viruses Can wait in memory until a
  program is run or act immediately by making
  copies of themselves.
• FAT Virus - This type of virus attack can be
  especially dangerous, by preventing access to
  certain sections of the disk where important
  files are stored. Damage caused can result in
  information losses from individual files or even
  entire directories.

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How can you get a virus?

• Downloading infected document files
• E-mail
• Being attached to a computer network with an
  infected computer
• Removable media

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Running executable programs

• A virus can only be contracted by a computer if
  it is in executable format- i.e. it must be
  contained within a program or document that the
  computer tries to run
• This includes Microsoft Word documents (.doc),
  Excel (.xls), PowerPoint (.ppt)
• When an application containing a virus is opened,
  the virus will continue to affect all other
  documents used by the same application
• Documents that are not executible (data files)
  are not considered harmful (eg. A picture with
  file extension .gif)

INFECTS
INFECTS
INFECTS
DOES NOT INFECT
INFECTS
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Removable Media

• Boot Sector Viruses are contracted from floppy
  discs. When the infected floppy disc is used in
  an attempt to boot your computer, the virus
  infects the hard drive. The virus uses the hard
  drive to spread to the rest of the system, and
  will attempt to infect any other floppy disc
  inserted.
• It is also possible for secondary storage devices
  storing published software applications to carry
  viruses, although most software companies perform
  virus scans to prevent this.

Infected floppy disc Inserted
Computer rebooted
Hard drive infected
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Being on a Network with an Infected Computer

• Networks provide more opportunities for viruses
  to enter and spread to multiple computers
• If computers in a network run off of a common
  hard disk, an infected hard disk allows for rapid
  transmission of the virus
• Some foms of malware are created especially for
  transmission across networks. These are able to
  crack firewalls and proxy servers (programs
  designed to regulate passage of files/documents
  into the network).

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E-mail

• There are 2 ways to catch a virus through email
• E-mail attachments Many viruses are carried in
  executable files or documents, attached in
  e-mails. One must open these files in order for
  the virus to have an effect.
• Viewing certain types of e-mails (less frequent)
  An e-mail written in HTML format can include
  script infected with a virus. These types of
  emails can transmit viruses as soon as they are
  opened.
• E-mail viruses are especially dangerous, as they
  can access a persons address book and send out
  virus replicates to many users at once.

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Preventing Viruses

• Steps to preventing viruses
• Dont open suspicious E-Mails

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Preventing Viruses

• Steps to preventing viruses
• Dont download suspicious files

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Antivirus Software

• Commercial Software
• Norton
• MacAfee
• Free Software
• Antivir
• AVG anti-virus

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Pros and Cons

• Pros and Cons of commercial software
• Pros
• Technical support included
• More people working to improve it
• Cons
• Cost
• Well known, so virus manufacturers can test
  created viruses on these programs to predict
  results

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Pros and Cons

• Pros and Cons of free software
• Pros
• Free
• Less known, so less likely to be tested against
• Cons
• Not as many people working to improve the
  programs
• No technical support