COMPUTER

SOFTWARE

VIRUSES

HARDWARE

A computer virus is a small software program that spreads from one

computer to another computer and that interferes with computer operation. A

computer virus may corrupt or delete data on a computer, use an e-mail program

to spread the virus to other computers, or even delete everything on the hard

disk.

Computer viruses are most easily spread by attachments in e-mail

messages or by instant messaging messages. Therefore, you must never open an

e-mail attachment unless you know who sent the message or unless you are

expecting the e-mail attachment. Computer viruses can be disguised as

attachments of funny images, greeting cards, or audio and video files. Computer

viruses also spread by using downloads on the Internet. Computer viruses can be

hidden in pirated software or in other files or programs that you may download.

What is Computer Virus..??

• BOOT VIRUSES :-

These viruses infect disc boot records or master boot records in hard disks. They

replace the boot record program (which is responsible for loading the operating system inmemory) copying it elsewhere on the disk or overwriting it. Boot viruses load into memoryif the computer tries to read the disk while it is booting.

Examples: Form, Disk Killer, Michelangelo, and Stone virus

• PROGRAM VIRUSES:-These infect executable program files, such as those with extensions like .BIN, .COM, .EXE, .OVL, .DRV (driver) and .SYS (device driver). These programs are loaded in memory during execution, taking the virus with them. The virus becomes active in memory, making copies of itself and infecting files on disk.Examples: Sunday, Cascade

VIRUSES – TYPES AND EXAMPLES

•Multipartite viruses:

A hybrid of Boot and Program viruses. They infect program files and when the infected program is executed, these viruses infect the boot record. When you boot the computer next time the virus from the boot record loads in memory and then starts infecting other program files on disk.Examples: Invader, Flip, and Tequila

• Stealth viruses:These viruses use certain techniques to avoid detection. They may either redirect the

disk head to read another sector instead of the one in which they reside or they may alter the reading of the infected file’s size shown in the directory listing. For instance, the Whale virus adds 9216 bytes to an infected file; then the virus subtracts the same number of bytes (9216) from the size given in the directory.Examples: Frodo, Joshi, Whale

• Polymorphic viruses:

A virus that can encrypt its code in different ways so that it appears differently in each infection. These viruses are more difficult to detect.Examples: Involuntary, Stimulate, Cascade, Phoenix, Evil, Proud, Virus 101

•Macro Viruses:-

A macro virus is a new type of computer virus that infects the macros within a document or template. When you open a word processing or spreadsheet document, the macro virus is activated and it infects the Normal template (Normal.dot)-a general purpose file that stores default document formatting settings. Every document you open refers to the Normal template, and hence gets infected with the macro virus. Since this virus attaches itself to documents, the infection can spread if such documents are opened on other computers.

Examples: DMV, Nuclear, Word Concept.

• Active X: -

ActiveX and Java controls will soon be the scourge of computing. Most people do not

know how to control there web browser to enable or disable the various functions like playing sound or video and so, by default, leave a nice big hole in the security by allowing applets free run into there machine. There has been a lot of commotion behind this and with the amount of power that JAVA imparts, things from the security angle seem a bit gloom

COMPUTER TROJANS

COMPUTER TROJANS ARE SIMPLY MALICIOUS COMPUTERPROGRAMS DISGUISED AS SOMETHING USEFUL.

THE MAJOR DIFFERENCE BETWEEN VIRUSES AND TROJANS IS THATVIRUSES REPRODUCE, WHILE A TROJAN IS JUST A ONE TIMEPROGRAM WHICH EXECUTES ITS PAYLOAD AS SOON AS THE TROJANIS EXECUTED

TROJANS ARE THE MOST COMMON WAY OF BRINGING A VIRUSINTO A SYSTEM.

A CURRENT EXAMPLE OF A TROJAN IS A PROGRAM CALLEDPKZ300B.EXE WHICH DISGUISES ITSELF AS AN ARCHIVING UTILITY,BUT WHEN RUN IT WILL DELETE YOUR ENTIRE HARD DRIVE.

Computer Worms are reproducing programs that run independantly and travel across network connections. The main difference between viruses and worms is the method in which they reproduce and spread. A virus is dependant upon a host file or boot sector, and the transfer of files between machines to spread, while a worm can run completely independently and spread of its own will through network connections.

An example of a worm is the famous internet worm of 1988: Overnight the worm copied itself across the internet, infecting every Sun-3 and VAX system with so many copies of itself that the systems were unusable. Eventually several sites disconnected themselves from the internet to avoid reinfection.

COMPUTER WORMS

Computer viruses usually spread in one of three ways:-

• From Removable media.

• From Downloads off the Internet.

• From e-mail attachments.

HOW DO COMPUTER VIRUSES SPREAD

Removable Disc

E-mail

Virus..

Computer is infected with a malicious computer virus, it may begin to show aseries of Computer Virus symptoms that indicate that a virus is present.

Computer viruses can be very harmful and damaging to your computer system,root files, and various program files. A computer virus can also increase the risk ofhacker threats and attacks, and open the door to even more unauthorizeddownloads and software installations.

When a virus begins to spread, many program files can become unstable anddisplay warnings.

The operating system may not launch properly, and the computer user may needto reboot and restart the computer frequently to ensure all programs are startingand working fine.

Critical files may get deleted automatically, and this can happen periodically or allat once. Error messages will become prevalent; it may become difficult to savedocuments, and the computer may be running slower than usual.

COMPUTER VIRUS SYMPTOMS

When a computer virus infects e-mail messages or infects other files on a computer, you may notice the following symptoms:

The infected file may make copies of itself. This behavior may use up all the free space on the hard disk.

A copy of the infected file may be sent to all the addresses in an e-mail address list.

The computer virus may reformat the hard disk. This behavior will delete files and programs.

SYMPTOMS OF WORMS AND TROJAN HORSE VIRUSES IN E-MAIL MESSAGES

A computer virus can do a lot of damage to your system before you even realize that it happened. Leaving your computer unprotected is a primary reason why most of the computer viruses get into your system.

Different types of computer viruses that invade your system. Scum ware, Adware, Spyware, Trojan Horses, computer viruses and Worms. Each one attacks your system in a similar way.

Computer Viruses: Quickly spreads from one computer to another computer. It starts by attaching and loading itself onto the computer without your knowledge.

A computer virus can be duplicated.

A COMPUTER VIRUS CAN DAMAGE YOUR SYSTEM

Install and Update the antivirus software on thecomputer. Then, perform a thorough scan of thecomputer by using the antivirus software.

Install the latest updates from Microsoft Update onthe computer.

Download, install, and then run the MaliciousSoftware Removal Tool to remove existing viruseson the computer. To download the MaliciousSoftware Removal Too

HOW TO REMOVE A COMPUTER VIRUS

On the computer, turn on the firewall.

Keep the computer operating system up-to-date.

Use updated antivirus software on the computer.

HOW TO PROTECT YOUR COMPUTER AGAINST VIRUSES

CONCLUSION..!!