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COMPUTER

Class 7 kindly read the notes of the chapter given below and do the exercises in your copy. COMPUTER

What is a ?

A computer virus is a program or a piece of code that is specifically designed to spread from computer systems to another computer and to interfere with computer operation without the knowledge of the victim.

Means of the Traversal of Virus

• travel through flash drives, CD drives, pen drives, World first virus was and , etc. written by 15 year old Rich Skrenta . • Virus code gets replicate when copied by users. The first virus for • Even documents (like Word, Excel, Notepad) do carry Viruses the personl when these files get affected. computer was “” created by Basit and Amjad

• is the most widespread method of sending virus to others. Foarroq Alvi.

Types of Computer virus

1. virus boot sector virus alters the boot sector program stored in the hard disk or any other storage device such as floppy disks. It replaces the boot sector program with its own malicious code.It enters into your system through corrupt media files, infected storage devices, and insecure computer networks. You need to format your system to get rid of Boot sector virus. Example : Disk killer and stone virus 2. Program file virus Some file/program when executed load the virus in the memory.They embeds itself into files and perform predefined functions to infect the system .They infect program files like .EXE, .COM, .BIN , .DRV , .SYS. Example : Sunday and 3. Polymorphic virus

It creates its thousands of copies itself and in each copy it changes the sequence and byte values to evade detection by antivirus .It take many different forms on your computer.It is very difficult to detect and remove this virus. Example: Phoenix and Evil 4. Overwrite virus It is the simplest computer virus that overwrites the code of the host computer system's file with its own malicious code .It destroys the original program code by overwriting it with its defective code. The infected files must be deleted or replaced with a new copy as this virus cannot be removed or disinfected.

Example : TRj. and Trivial.88.D

5. Spacefiller virus The Spacefiller Virus is also known as Cavity Virus.It enters inside the file and occupies the empty spaces between the files. Example :CIH and Lehigh 6. Multipartite virus Multipartite virus spreads and infects in multiple ways. It infects both the boot sector and the executable files stored on the hard drive simultaneously. Example :Ghostball and Flip 7. virus Micro virus infects MS Word or similar application and cause a sequence of actions to be performed automatically ,when the application started or something else triggered. Example : Nuclear and worm

Symptoms of a Computer Virus

There are many symptoms which show that a computer is infected with a virus, some of which are as follows: o Slow computer performance: The machine may work slowly, e.g., it will take more time to open or shut down the computer or while opening a file, document, computer application, etc. The and internet speed may get slow. o Frequent pop-ups: A virus may cause unusual frequent pop-ups on your window. o Hard Drive issue: The hard drive may exhibit unusual high activity even when it is not in use. It may cause unwanted changes to your hard drive and may freeze or this device.

o Frequent crashes: One may experience frequent sudden system crashes while playing games, watching videos, or doing some other work using the infected system. A blue screen appears when it crashes. o Unknown programs: Unwanted programs may open or start automatically when you start your computer. You can see these programs in your computer's list of active applications. Sometimes, the window shuts down unexpectedly without any reason. o Unusual activities: Your machine may perform differently, such as you may not be able to log into your accounts, to delete the corrupt files, and Blue (BSOD) may appear frequently, and more. Furthermore, the hardware, software, or OS may start malfunctioning leading to crashing the system abruptly. o Impaired solutions: Sometimes, security measures taken by you, such as antivirus may not work smoothly due to virus attack on your computer. o Network issue: Sometimes, you experience high network activity even if you are not connected to the internet and vice versa. o Unnecessary advertisement: We often see advertisements while browsing, but if you see them even when you are not browsing, it may indicate a virus on your computer. o Display problems: You may experience different colors in your display if your computer is affected by a virus. o Unwanted to contacts: Many viruses take control of your of your email and start sending to people of your contact list. o Blocked by Antivirus Sites: An antivirus site may deny access to a computer that is infected by a virus. o Dialog Boxes: Many dialog boxes keep appearing suddenly on your screen. o Printer Issues: A printer attached to an infected computer may print documents without getting any command or in an inappropriate manner.

What are the harm caused by Virus ?

ü Slow down computer performance. ü It might corrupt System files. ü Virus may use all internet without knowledge. ü Hardware attached to computer behave erratically. ü Sensitive information like bank details can be stolen from computer system.

How to prevent Virus attack ?

ü Never open a mail with attachments from unknown site or Bernd Fix user ID. was the ü Do not trust a pen drive from an unknown source.Always first person to scan it before using on computer . remove a ü Do not download software from untrusted site on the virus in internet. 1987. ü Use and keep it updated. Windows ü Instantly leave website you have been routed to without defender is an your consent. inbuilt ü Do not let unknown people use your computer. virus protectio What is an Antivirus? Features of an antivirus software n system in Antivirus is a software that is used to detect and remove virus.It is Windows operating capable ofmonitoring your computer system,incoming data through system. the internet,external storage devices like pen drive,email to protect

The term computer from virus attack. virus was coined by Features of an antivirus software American computer ü Interface-the interface must be easy to understand and scientist use. Fredrick B Cohen in ü Resources required-Antivirus software should not use lot of 1983. computer resources. ü Price-price of the software must be reasonable.

Examples of antivirus for Windows system are: security premium,McAfee Antivirus,Symantec Antivirus AVG , Antivirus, Antivirus, Kaspersky free Antivirus,Panda Free antivirus

There are certain terms used to describe malicious software that has infiltrated your computer through the Internet. Let’s take a look at how it happens-

ü The term « malware » or « malicious software » is used for any type of software that can affect your computer equipment’s performance and functionality, either locally or remotely. Computer viruses, Trojan horses and worms are all considered malware .

ü Worm A infiltrates your computer when you download a file or an email. The worm then clones itself and attacks other devices on your network. The worm will infect your files, and will spread to the of people who you communicate with, in the same way that it infiltrated your computer. Worms uses lots of internet bandwidth. Example :I LOVE YOU and Michelangelo

ü Virus

A virus infects « host » files on your computer, and then it is transmitted to other users when you send out those files. This is how computer viruses spread. The virus’ effects may vary from decreased computer performance to a complete loss of the computer’s functionality.

The difference is that a worm operates more or less independently of other files, whereas a virus depends on a host program to spread itself.

ü Spyware spies on everything you do: paying your bills online, watching online videos, using Facebook, etc. It compiles this information and sends it to a that then affects your web browsing. Depending on your preferences and your browsing history, the database will suggest « promotional offers » or other scams. Spyware can also download and install viruses on your computer or open « pop-up » when you are surfing the web. Example: keyloggers and website cookies.

ü A Trojan horse or « Trojan », infiltrates your computer through a file that you download and open. Unlike viruses, most Trojans stay on your computer only. They cause damage, but they do not spread to other computers. A Trojan is a piece of malware that stays in one place rather than spreading.It hides a worm or virus inside it. Example : Trojun.

ü Virus Sweeper

A virus sweeper is a fake antivirus.It disguises itself as antivirus.When users click on ads ,this virus installs itself on the system.

Example : Antivirus 2009,Vista Antivirus EXERCISES

Q1.Answer in one word-

a) Which software acts against a virus b) Formatting system helps to get rid of which virus. c) Which virus take different forms on your system. d) Which is the most widespread method of sending viruses to others. e) Michelangelo is an example of which malicious code. f) Which can hide a virus within it. g) Name a virus that enter inside the file. h) Which virus is difficult to remove. i) Give an example of Spyware. j) Name any two Antivirus software.

Q2. What do you understand by program virus?

Q3.What is the difference between virus and worm?

Q4.Give three ways in which virus can harm your computer?

Q5.What are the factors that must be considered while choosing an antivirus?

Q6.How to prevent virus attack?

Q7.Write short notes on the following-

• Malware • Spyware • Trojan horse