produced by unknown people and harmful to the computers
Some varieties of these software are the
Viruses , Worms and Trojan horses
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.
Trojan horse perform a desirable function for the user in addition to the expected function
Usually does not reproduce
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.
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
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
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 website.
Unix Shell Scripts
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
02/28/12 Releasing computer viruses is a crime in most jurisdictions
File infector virus
Infect program files
Boot sector virus
Infect the system area of a disk
Master boot record virus
infect disks in the same manner as boot sector viruses. The difference between these two virus types is where the viral code is located.
Infect both boot records and program files.
Infect data files. Example: Microsoft Office Word, Excel,
PowerPoint and Access files
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
Melissa Virus was the fastest spreading virus ever seen.
Forced a number of large companies to shut down their e-mail systems.
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.
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.
Designed to do three things
Replicate itself for the first 20 days of each month
Replace web pages on infected servers with a page that declares “Hacked by Chinese”
Launch a concreted attack on the White House Web server.
The Morto virus emerged in the summer of 2011.
It attempts to propagate itself to additional computers via the Remote Desktop Protocol
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.
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
They kill the tasks associated with antivirus
software before it can detect them.
Take regular backups (including OS) on different media, unconnected to the system (most of the time)
02/28/12 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 unusable.
02/28/12 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
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
Backup your files on a regular basis
Always scan new files for viruses before you use them
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