Computer virus

Computer VirusComputer Virus

What is a Computer VirusWhat is a Computer Virus

• A kind of software programs

– produced by unknown people and harmful to

the computers

• Some varieties of these software are the

– Viruses, Worms and Trojan horses

What is a Computer VirusWhat is a Computer Virus

• The term “Virus" is often used in common

– to describe all kinds of malware (malicious

software)

Damages done by VirusesDamages done by Viruses

• Sometimes display unwanted messages

• Some tend to destroy programs or data

• Clog computer memory and hence sometimes result in

system crashes

• Format hard disks, Damage programs, Delete files

Viruses

Damages done by VirusesDamages done by Viruses

• Simply replicate themselves

• Presents text, video, or audio messages making the user

know their presence

• Bug-ridden, and these bugs may lead to system crashes

and data loss

Virus spreading methodsVirus spreading methods

• A viruses can copy itself and infect a computer

– without permission or knowledge of the user

• attaches itself to other software programs or

data files


• Spreads from computer to computer when the

host is taken to the uninfected computer

– over a network such as over the Internet or carrying it on a

removable medium - a floppy disk, CD, or USB drive


• Many viruses are existed in the Internet today

and new ones are discovered every day.

– spread via downloaded software and data files, and

email attachments, etc


• Some old viruses are installed themselves

into the disk boot sector

– runs when the user boot the computer from

the disk


• Some viruses spread through instant messaging

– A virus, in an infected machine, may send a web-address-

link as a message to other contacting machines

– Thinking the link is from a friend (a trusted source), the

recipient may sometimes follow the link to the websit.


• Some viruses Transmitt through instant messaging

– A virus, in an infected machine, may send a web-address-link as

a message to other contacting machines

– Thinking the link is from a friend (a trusted source), the recipient

may sometimes follow the link to the website

– The virus can then easily infects this new computer and continue

propagating.

How Viruses are borneHow Viruses are borne

• Unlike biological viruses, computer viruses

do not simply evolve by themselves

– deliberately created by programmers, or by

people who use virus creation software


• Viruses are written as

– research projects, pranks, vandalism,

– to attack the products of specific companies,

– to distribute political messages,

– and financial gain from identity theft,

– spyware, and cryptoviral extortion.


• Some virus writers

– consider their creations to be works of art

– See virus writing as a creative hobby

Releasing computer viruses is a crime in most jurisdictions

Viruses can avoid detectionViruses can avoid detection

• To avoid detection by users, viruses employ

different deception methods

– They do not make themselves to

• change the date of last modified

• increase file sizes

• damage the files

Viruses can avoid detectionViruses can avoid detection

– They kill the tasks associated with antivirus

software before it can detect them

How Antivirus software works?How Antivirus software works?

• Detect using a list of virus signature definitions

– comparing the files stored on fixed or removable

drives (hard drives, floppy drives), against a database

of known virus "signatures".


• Use a heuristic algorithm to find viruses based

on common behaviors

– Examin the content heuristics of the computer's

memory (its RAM, and boot sectors)


• Some anti-virus programs gives you a

real time protection

– Examin files as they are being opened,

downloaded, copied, accessed, and

transmitted etc


• They need regular updates

– in order to gain knowledge about the

latest threats

Damage prevention & data recoveringDamage prevention & data recovering

• Take regular backups (including OS) on different

media, unconnected to the system (most of the

time)

How to prevent damages caused by viruses?

Damage prevention & data recoveringDamage prevention & data recovering

• Use backups on optical media like CD and DVD

(read-only), as they can no longer be affected by

viruses.

• Use an OS on a bootable, to start the computer

if the installed OS become unusable.

How to prevent damages caused by viruses?

Keep your computer Virus freeKeep your computer Virus free

• Install reliable anti-virus software

– the most important step you can take towards keeping

your computer clean of viruses

• Update your anti-virus software regularly

– variations of viruses and new ones can be slipped if your

software is not current


• Get immediate protection

– Configure your anti-virus software to boot automatically on

start-up and run at all times


• Don't automatically open attachments

– ensure that you examine and scan email and other

attachments before they run as they might contain viruses

• Scan all incoming email attachments

– Do not open any email attached files if the subject line is

questionable, unexpected or the source (address) is

unknown, suspicious or untrustworthy


• Delete chain emails and junk email

– Do not forward or reply to any of them, they clogs up the

network

– Some viruses can replicate themselves and spread

through email as a chain


• Be careful when downloading files from the

Internet

– Ensure that the source is a legitimate and reputable one

– save all downloads to one folder and test them with your

own anti-virus software before use


• Always scan new files for viruses before you

use them


• Backup your files on a regular basis


• If your computer is on a network, make sure

you have security steps in place to prevent

unauthorized users putting files on your

computer


• Take care using USB flash cards, CDs, zip

and floppy disks

– The more computers flash cards, CDs, zip cards and

floppies have been used on, the better the chance of a

virus infecting them – clean them before use

Technology

Computer virus