Computer Viruses (A small Review)

Use Internet Security for protecting your computer

 VIRUS(Vital Information Resources Under Siege).

 Strange as it may sound, the computer virus is something of an Information Age marvel. On one hand, viruses show us how vulnerable we are -- a properly engineered virus can have a devastating effect, disrupting productivity and doing billions of dollars in damages. On the other hand, they show us how sophisticated and interconnected human beings have become.
For example, experts estimate that the Mydoom worm infected approximately a quarter-million computers in a single day in January 2004. Back in March 1999, the Melissa virus was so powerful that it forced Microsoft and a number of other very large companies to completely turn off their e-mail systems until the virus could be contained. The ILOVEYOU virus in 2000 had a similarly devastating effect. In January 2007, a worm called Storm appeared -- by October, experts believed up to 50 million computers were infected. That's pretty impressive when you consider that many viruses are incredibly simple.
When you listen to the news, you hear about many different forms of electronic infection. The most common are:

•  Viruses - A virus is a small piece of software that piggybacks on real programs. For example, a virus might attach itself to a program such as a spreadsheet program. Each time the spreadsheet program runs, the virus runs, too, and it has the chance to reproduce (by attaching to other programs) or wreak havoc.
• E-mail viruses - An e-mail virus travels as an attachment to e-mail messages, and usually replicates itself by automatically mailing itself to dozens of people in the victim's e-mail address book. Some e-mail viruses don't even require a double-click -- they launch when you view the infected message in the preview pane of your e-mail software.
• Trojan horses - A Trojan horse is simply a computer program. The program claims to do one thing (it may claim to be a game) but instead does damage when you run it (it may erase your hard disk). Trojan horses have no way to replicate automatically.
• Worms - A worm is a small piece of software that uses computer networks and security holes to replicate itself. A copy of the worm scans the network for another machine that has a specific security hole. It copies itself to the new machine using the security hole, and then starts replicating from there, as well.

In this article, we will discuss viruses -- both "traditional" viruses and e-mail viruses -- so that you can learn how they work and understand how to protect yourself. 

Use Anitvirus or Internet Security...

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What happens when WE switch ON the Computer (Booting)

Booting or loading an operating system is different than installing it, which is generally an initial one-time activity. (Those who buy a computer with an operating system already installed don't have to worry about that.) When you install the operating system, you may be asked to identify certain options or configuration choices. At the end of installation, your operating system is on your hard disk ready to be booted (loaded) into random access memory, the computer storage that is closer to the microprocessor and faster to work with than the hard disk. 

Typically, when an operating system is installed, it is set up so that when you turn the computer on, the system is automatically booted as well. If you run out of storage (memory) or the operating system or an application program encounters an error, you may get an error message or your screen may "freeze" (you can't do anything). In these events, you may have to reboot the operating system.

How Booting Works 

(Note: This procedure may differ slightly for Mac, UNIX, OS/2, or other operating systems.) 

 

When you turn on your computer, chances are that the operating system has been set up to boot (load into RAM) automatically in this sequence:

1. As soon as the computer is turned on, the basic input-output system (BIOS) on your system's read-only memory (ROM) chip is "woken up" and takes charge. BIOS is already loaded because it's built-in to the ROM chip and, unlike random access memory (RAM), ROM contents don't get erased when the computer is turned off.
2. BIOS first does a power-on self test (POST) to make sure all the computer's components are operational. Then the BIOS's boot program looks for the special boot programs that will actually load the operating system onto the hard disk.
3. First, it looks on drive A (unless you've set it up some other way or there is no diskette drive) at a specific place where operating system boot files are located. If there is a diskette in drive A but it's not a system disk, BIOS will send you a message that drive A doesn't contain a system disk. If there is no diskette in drive A (which is the most common case), BIOS looks for the system files at a specific place on your hard drive.
4. Having identified the drive where boot files are located, BIOS next looks at the first sector (a 512-byte area) and copies information from it into specific locations in RAM. This information is known as the boot record or Master Boot Record.
5. It then loads the boot record into a specific place (hexadecimal address 7C00) in RAM.
6. The boot record contains a program that BIOS now branches to, giving the boot record control of the computer.
7. The boot record loads the initial system file (for example, for DOS systems, IO.SYS) into RAM from the diskette or hard disk.
8. The initial file (for example, IO.SYS, which includes a program called SYSINIT) then loads the rest of the operating system into RAM. (At this point, the boot record is no longer needed and can be overlaid by other data.)
9. The initial file (for example, SYSINIT) loads a system file (for example, MSDOS.SYS) that knows how to work with the BIOS.
10. One of the first operating system files that is loaded is a system configuration file (for DOS, it's called CONFIG.SYS). Information in the configuration file tells the loading program which specific operating system files need to be loaded (for example, specific device driver.
11. Another special file that is loaded is one that tells which specific applications or commands the user wants to have included or performed as part of the boot process. In DOS, this file is named AUTOEXEC.BAT. In Windows, it's called WIN.INI.
12. After all operating system files have been loaded, the operating system is given control of the computer and performs requested initial commands and then waits for the first interactive user input.

 

 

What are All the Buttons, Sockets, and Slots Used For?

Take a look at the front and back of your computer case and count the number of buttons, sockets, and slots you see. Now, look at your monitor and count any that appear there. You probably counted approximately 20.
Each computer is different, therefore the buttons, slots, and sockets will vary from computer to computer; however, there are certain features you can expect to find on most desktop computers. Being familiar with the names of each and how they are commonly used will help you when the time comes for you to connect that new printer, mouse, digital camera, or other device.  

Front of Computer Case

1. Power Button
   The power button is used to power the computer on and off. Additionally, you can use the power button on some computers to place the computer in different energy-saving modes such as hibernate, sleep, and standby. It is a good idea to read your manual to learn how these features work on your computer.
2. CD-ROM (Compact Disk Read-Only Memory) Drive
   A CD-ROM drive, also known as an optical drive, allows you to play a CD-ROM , just like a CD player allows you to listen to music. With a CD-ROM drive you can listen to music (if your computer is sound-enabled), view files, and install software that is located on a CD.
   
   A CD writer is a device that can be used in conjunction with a CD-ROM drive and allows you to copy or burn information onto specific types of CDs called CD-RW (Compact Disk ReWritable) and CD-R (Compact Disk-Recordable) discs.
3. DVD-ROM (Digital Versatile Disc Read-Only Memory) Drive
   A DVD-ROM drive, also known as an optical drive, reads DVD discs, all types of CDs, and can display movies from digital video discs. DVDs can hold more data than a CD, so they are a good storage option. A DVD burner is a device that can be used in conjunction with a DVD-ROM and allows you to copy information onto DVD discs. It is considered a type of storage.
4. USB Port
   The Universal Serial Port typically appears on the back of the computer case, but can sometimes be found on the front of the case, or hidden under a panel on the front of the case.
5. Audio In/Audio Out Every computer has a bank of audio ports where you can connect various devices, including speakers, microphones, headsets, and more.

Back of Computer Case

On the back of the computer case are connection ports that are made to fit specific devices. The arrangement of these vary from computer to computer, and many companies have their own special connectors for the specific devices. Some of the ports are color coded to match a color on the device, which will help you determine which port is used with a particular device.

1. PS/2 Port
   These ports are called PS/2 ports and are used for the mouse and keyboard. Many people refer to them as the mouse port or the keyboard port.
2. Ethernet Port
   This port looks a lot like the modem or telephone port but it is actually wider. You can use this port for networking and also connecting to the Internet.
3. Audio In/Audio Out
   Every computer has a bank of audio ports where you can connect various devices, including speakers, microphones, headsets, and more.
4. VGA Port
   Your monitor is connected to this port.
5. USB Port
   The Universal Serial Bus port is one of the newest ports, but is also one of the most useful. These USB ports let you attach a variety of devices such as mice, printers, keyboards, web cameras, USB/flash drives, and digital cameras to your computer quickly. Almost every peripheral made comes in a USB version, and installing the devices using USB ports is much easier than connecting devices using parallel and serial ports. This is primarily because USB ports do not require you to reboot your computer before you can use the new device.

1. Parallel Port
   The parallel port is one of the two original ports on the first personal computer. It is commonly known as the printer port since this port is used to connect your printer to your computer; however, with the rise in use of the USB ports, you can expect to see a decrease in the use of this port. Currently, a large number of parallel port printers are still manufactured and used on older computers that don’t have USB support.
2. Serial Port
   The serial port is the other original port on the first personal computer. Serial ports can be used to plug in devices such as dial-up modems and other devices. On recent computers, the serial port has been replaced by the USB port. This is due to the fact that most peripherals use the USB drive.
3. Expansion Slots
   These empty slots are where expansion cards are added to computers. For example, if your computer did not come with a video card, you could purchase one and insert it here.
4. FireWire Port
   FireWire is actually the Apple brand name for the IEEE 1394 port, but the term caught on and it this port is commonly referred to as the FireWire port. It is the standard port used with digital video cameras and high-resolution scanners. FireWire replaced the Parallel SCSI, but it is not on every computer; however, you can buy an adapter card to add FireWire ports to your computer. The labeled image does not include a FireWire port.

Peripherals You Can Use in Various Ports

PDA

Printer

Webcam

Headphone

• Printers: A printer is a peripheral that is used to print, or produce, a version of what appears on the screen in a hardcopy format. There are many types of printers available including ink-jet, laser-jet, and photo printers. Also, combination printers that include scanners and copiers are increasing in popularity.
• Scanners: A scanner allows you to copy an image or document and save it in electronic form onto your computer. While you can purchase a hand-held and flatbed scanners, you are more likely to purchase a scanner as an all-in-one option that combines a scanner, printer, and copier into one product.
  Scanners vary in resolution, or sharpness, so when shopping for one, be sure to compare the resolution of the products. A scanner is connected to the computer via a parallel port, a USB port, or a SCSI connection. No matter which connection is used, the images are stored on your PC's hard drive in a digital format. 
• Speakers/Headphones: Speakers and headphones are output devices, which means that they are devices that communicate information from the computer to the user. They allow you to hear sound and music. Both speakers and headphones connect to a computer; however, some computers are designed with speakers built into the monitor.
• Microphones: A microphone is a type of input device, or a device that receives information from a user. You connect the microphone to the computer and use the computer to record sound or to communicate with another computer user via the Internet. Many computers come with built-in microphones.
• Web Cameras: Web cameras, or web cams, are devices that connect to a computer and display a video image of whatever it is recording. This video image can be transmitted over the Internet, allowing a user in another location to see the video in real-time. Web cameras are used often in business for video conferences, and are also a great tool for families to use to stay connected from different parts of the world.
• Joystick or Game Controller: A joystick is a lever used while playing a computer game.
• Digital Cameras: A digital camera lets you capture a picture in digital (computer-readable) form. You can transfer that image directly from the camera to the computer. When you use a digital camera, you can also preview your pictures before printing them. If you don't like what you see, you can edit or delete them.
• Personal Digital Assistant (PDA): A PDA is a handheld computer that can have a variety of features including a calendar, Internet access, video recording, word processing, email access, phone, media player, and more. Most PDAs can be synchronized with a PC to allow up-to-date contact information stored on software such as Microsoft Outlook, RSS feeds, or other web updates.
• MP3 Players: An MP3 player is a portable device that stores, organizes, and plays audio files. The player can read files that are recorded from a CD using a computer, or downloaded from various sites via the Internet.

 

 

Parts of a Computer

There are mainly three parts of computer: 

(1) INPUT DEVICE: Those device through which we can input our data.

Example:Keyboard,Mouse,Joystick,OCR(Optical Character Redear),OMR(Optical Mark Redear),MICR(Magenetic Ink Character Redear),etc.

(2) CPU(Central Processing Unit):Central Processing Unit - (CPU, processor) The part of a computer which controls all the other parts. Designs vary widely but the CPU generally consists of the control unit, the arithmetic and logic unit (ALU), registers, temporary buffers and various other logic.

The control unit fetches instructions from memory and decodes them to produce signals which control the other parts of the computer. These signals cause it to transfer data between memory and ALU or to activate peripherals to perform input or output.

Various types of memory, including cache, RAM and ROM, are often considered to be part of the CPU, particularly in modern microprocessors where a single integrated circuit may contain one or more processors as well as any or all of the above types of memory. The CPU, and any of these components that are in separate chips, are usually all located on the same printed circuit board, known as the motherboard. This in turn is located in the system unit (sometimes incorrectly referred to as the "CPU").

A parallel computer has several CPUs which may share other resources such as memory and peripherals.

The term "processor" has to some extent replaced "CPU", though RAM and ROM are not logically part of the processor.

(3) Output Device: Those device through which we can take or print our data.

Example: V.D.U.(Visual Display Unit) or Monitor,Printer,Plotter,Speaker,etc.

What is Drivers?

Drivers

A program that controls a device. Every device, whether it be a printer, disk drive, or keyboard, must have a driver program. Many drivers, such as the keyboard driver, come with the operating system. For other devices, you may need to load a new driver when you connect the device to your computer. In Dos systems, drivers are files with a.SYS extension. In Windows-environments, drivers often have a.DRV extension.

A driver acts like a translator between the device and programs that use the device. Each device has its own set of specialized commands that only its driver knows. In contrast, most programs access devices by using generic commands. The driver, therefore, accepts generic commands from a program and then translates them into specialized commands for the device.

Operating System

 

The most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers.

For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop -- it makes sure that different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system.

Operating systems can be classified as follows:

• Multi-user : Allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users.
• Multiprocessing : Supports running a program on more than one CPU.
• Multitasking : Allows more than one program to run concurrently.
• Multithreading : Allows different parts of a single program to run concurrently.
• Real time: Responds to input instantly. General-purpose operating systems, such as DOS and UNIX, are not real-time.

Operating systems provide a software platform on top of which other programs, called application programs, can run. The application programs must be written to run on top of a particular operating system. Your choice of operating system, therefore, determines to a great extent the applications you can run. For PCs, the most popular operating systems are DOS, OS/2, and Windows, but others are available, such as Linux.

As a user, you normally interact with the operating system through a set of commands. For example, the DOS operating system contains commands such as COPY and RENAME for copying files and changing the names of files, respectively. The commands are accepted and executed by a part of the operating system called the command processor or command line interpreter. Graphical user interfaces allow you to enter commands by pointing and clicking at objects that appear on the screen.

computer

A programmable machine. The two principal characteristics of a computer are:

It responds to a specific set of instructions in a well-defined manner.

It can execute a prerecorded list of instructions (a program).

Modern computers are electronic and digital. The actual machinery -- wires,transistors, and circuits -- is called hardware; the instructions and data are called software.

All general-purpose computers require the following hardware components:

memory : Enables a computer to store, at least temporarily, data and programs.

mass storage device : Allows a computer to permanently retain large amounts of data. Common mass storage devices include disk drives and tape drives.

input device : Usually a keyboard and mouse, the input device is the conduit through which data and instructions enter a computer.

output device : A display screen, printer, or other device that lets you see what the computer has accomplished.

central processing unit (CPU): The heart of the computer, this is the component that actually executes instructions.

In addition to these components, many others make it possible for the basic components to work together efficiently. For example, every computer requires a bus that transmits data from one part of the computer to another.

Computers can be generally classified by size and power as follows, though there is considerable overlap:

personal computer : A small, single-user computer based on a microprocessor. In addition to the microprocessor, a personal computer has a keyboard for entering data, a monitor for displaying information, and a storage device for saving data.

workstation : A powerful, single-user computer. A workstation is like a personal computer, but it has a more powerful microprocessor and a higher-quality monitor.

minicomputer : A multi-user computer capable of supporting from 10 to hundreds of users simultaneously.

mainframe : A powerful multi-user computer capable of supporting many hundreds or thousands of users simultaneously.

supercomputer : An extremely fast computer that can perform hundreds of millions of instructions per second.

courtesy:www.webopedia.com