Viruses, Worms, Trojans and

ANTIVIRUSES

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 or consent.

Types of viruses

• Boot viruses

• Program viruses

• Multipartite viruses

• Stealth viruses

• Polymorphic viruses

How viruses get into computers• 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

unknown senders.

• 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 Inbox

• 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 being opened:– .exe– .pif– .bat– .vbs– .com

ANTIVIRUS

• 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.

2009 AntiVirus Software Product Comparisons

Removal Of Some Common Viruses

• You can remove some of the common viruses without help of any antivirus Program.

• Eg : New Folder.exe

• Autorun.inf ( from PDs etc)

New Folder.exe• 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 them all.

Removal of Autorun.inf

• Open Run dialog Box. Type in “CMD” press ENTER.

• The Command Prompt will Open Now. In Command prompt go to the drive containing Autorun.inf

• 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.