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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

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The term “Virus" is often used in

common

to describe all kinds of malware (malicious

software) including  adware  and

spyware programs that do not have the

reproductive ability.

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Trojan horse perform a desirable function for the user in addition to the expected function

Leaks information Usually does not reproduce

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A worm is a self replicating malware computer program, which uses a computer network to send copies of itself to other computers and it may do so without any user intervention. It does not need to attach itself to an existing program.

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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

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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

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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 04/12/23 8

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

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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.

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Some old viruses are installed

themselves into the disk boot sector

runs when the user boot the computer from

the disk

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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 website.

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ANSI COBOL C/C++ Pascal VBA Unix Shell Scripts Javascript

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Unlike biological viruses, computer

viruses do not simply evolve by

themselves

deliberately created by programmers, or by

people who use virus creation software

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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.

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Some virus writers

consider their creations to be works of art

See virus writing as a creative hobby

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Releasing computer viruses is a crime in most

jurisdictions

File infector virusInfect program files

Boot sector virusInfect the system area of a disk

Master boot record virusinfect disks in the same manner as boot sector

viruses. The difference between these two virus types is where the viral code is located.

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Multi-partite virusInfect both boot records and program files.

Macro virusInfect data files. Example: Microsoft Office Word,

Excel,

PowerPoint and Access files

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Melissa virus spread in Microsoft Word documents sent via e-mail.

How it works ? Created the virus as word document Uploaded to an internet newsgroup Anyone who download the document and

opened it would trigger the virus. Send friendly email messages to first 50

people in person’s address book

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Melissa Virus was the fastest spreading virus ever seen.

Forced a number of large companies to shut down their e-mail systems.

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Contained a piece of code as an attachment.

Double Click on the attachment triggered the code.

Sent copies of itself to everyone in the victim’s address book

Started corrupting files on the victim’s machine.

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Code Red made huge headlines in 2001 It slowed down internet traffic when it

began to replicate itself. Each copy of the virus scanned the

internet for Windows NT or Windows 2000 that don’t have security patch installed.

Each time it found an unsecured server, the virus copied itself to that server.

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Designed to do three things

Replicate itself for the first 20 days of each monthReplace web pages on infected servers with a page that declares “Hacked by Chinese”Launch a concreted attack on the White House Web server.

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The Morto virus emerged in the summer of 2011.

It attempts to propagate itself to additional computers via the Remote Desktop Protocol

(RDP). Morto spreads by forcing infected systems

to scan for servers allowing RDP login.  Once Morto finds an RDP-accessible

system, it attempts to log in to a domain or local system account named 'Administrator' using a number of common passwords.

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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

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They kill the tasks associated with antivirus

software before it can detect them.

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Take regular backups (including OS) on

different media, unconnected to the

system (most of the time)

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How to prevent damages caused by viruses?

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

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How to prevent damages caused by viruses?

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

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Get immediate protection

Configure your anti-virus software to boot

automatically on start-up and run at all times

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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

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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

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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

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Backup your files on a regular basis

Always scan new files for viruses

before you use them

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If your computer is on a network,

make sure you have security steps in

place to prevent unauthorized users

putting files on your computer

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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

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