What is a virus?
• A computer virus is a computer program
that can copy itself and infect a computer
without permission or knowledge of the user.
• A virus can only spread from one computer to
another when its host is taken to the
uninfected computer, for instance by a user
sending it over a network or the Internet, or
by carrying it on a removable medium such
as a floppy disk, CD, or USB drive.
What is a WORM ?
• A computer worm is a self-replicating computer
program. It uses a network to send copies of itself to
other nodes (computer terminals on the network) and
it may do so without any user intervention.
• Unlike a virus, it does not need to attach itself to an
existing program. Worms almost always cause harm
to the network, if only by consuming bandwidth,
whereas viruses almost always corrupt or modify files
on a targeted computer.
What are Trojan Horses ?
• A Trojan horse, also known as a trojan, is malware
that appears to perform a desirable function but in
fact performs undisclosed malicious functions.
Therefore, a computer worm or virus may be a Trojan
horse. The term is derived from the classical story of
the Trojan Horse.
• A program named "waterfalls.scr" serves as a simple
example of a trojan horse. The author claims it is a
free waterfall screen saver. When run, it instead
unloads hidden programs, commands, scripts, or any
number of commands without the user's knowledge
Types of viruses
How viruses get into
The four most common virus infections come from:
– File – A virus type that infects existing files on the computer
(approx. 40% of all viruses)
– Macro – A virus that runs as a macro in a host application
such as the MS Office applications (approx. 35%)
– VBScript – A virus that uses Windows VisualBasic Script
functionality (approx. 10%)
– Internet Worm – A virus that is primarily characterized by
it’s replication across the Internet (approx. 5%)
Basic virus defense
Be cautious of files that you are not expecting and from
Many viruses automatically send files without the email account
owner’s knowledge. They can ‘piggyback’ on the email accounts
of senders you know.
Be suspicious of messages that appear more than once in your
• Be aware of sites offering free software downloads
Basic virus defense (cont.)
• Learn file extensions
– Your computer will display both an icon and a file
extension for every file.
– Open only file extensions you know are safe.
Examples of risky file types
• The following file types should be treated with
suspicion and be confirmed with the sender before
• Antivirus software are computer programs that
attempt to identify, neutralize or eliminate malicious
software. The term "antivirus" is used because the
earliest examples were designed exclusively to
combat computer viruses; however most modern
antivirus software is now designed to combat a wide
range of threats, including worms, phishing attacks,
Trojans, often described collectively as malware.
Removal Of Some Common Viruses
• You can remove some of the common
viruses without help of any antivirus
• Eg : New Folder.exe
• Autorun.inf ( from PDs etc)
It looks just like an folder but actually it is a exe file.
Step 1: Try deleting the file.
It will delete if you haven’t executed it, if you’re unable to delete it
Go to Task manager ( by pressing ctrl+shift+esc )
Go to Process Tab and
try finding that the
process for the exe file
and end the process.
Then Go to the same
folder containing the
exe file and delete it.
Then Open Search and
try finding the .exe files
of same size and delete
Removal of Autorun.inf
• Open Run dialog Box. Type in “CMD”
The Command Prompt will Open Now. In Command prompt go to the drive
Now Type In “ attrib –h –s –a” and press enter.
This will remove drives attributes for all Hidden, System files.
Now Type “ Delete autorun.inf” and press Enter.
The Virus has been Successfully Removed.