Computer Software
Software is a set of instructions, data or programs used to operate computers and execute specific tasks.
Opposite of hardware, which describes the physical aspects of a computer, software is a generic term used to refer to applications, scripts and programs that run on a device.
Software is often divided into two parts:
I) application software, or user downloaded programs that fulfill a want or need of users.
II) System software, which includes operating systems and any program that supports application software.
The term middleware is sometimes used to describe programming that mediates between application and system software or between two different kinds of application software. For example, middleware could be used to send a remote work request from an application in a computer that has one kind of operating system to an application in a computer with a different operating system.
An additional category of software is the utility which is a small, useful program with limited capability. Some utilities come with operating systems. Like applications, utilities tend to be separately installable and capable of being used independently from the rest of the operating system.
Similarly, applets are small applications that sometimes come with the operating system as accessories. They can also be created independently using the Java or other programming languages.
Software can be purchased or acquired in the following ways:
· Shareware- usually distributed on a free or trial basis with the intention of sale when the period is over.
· Liteware- a type of shareware with some capabilities disabled until the full version is purchased.
· Freeware- can be downloaded for free but with copyright restrictions.
· Public domain software- can be downloaded for free without restrictions.
· Open source- a type of software where the source code is furnished and users agree not to limit the distribution of improvements.
Today, much of the purchased software, shareware and freeware is directly downloaded over the Internet. In these cases, software can be found on specific vendor websites or application service providers. However, software can also be packaged on CD-ROMs or diskettes and sold physically to a consumer.
Some general kinds of application software include:
· Productivity software, which includes tools such as word processors and spreadsheets.
· Presentation software, also known as slideware.
· Graphics software.
· CAD/CAM.
· Vertical market or industry-specific software, for example, banking, insurance and retail applications.
A specialized type of software that allows hardware to run is firmware. This is a type of programming that is embedded onto a special area of the hardware's nonvolatile memory such as a microprocessor or read-only memory, on a one-time or infrequent basis so that thereafter it seems to be part of the hardware.
Virus & Anti-virus
1. What is a Virus?
ØComputer virus is a software program written with malicious intentions. ØComputer virus is a harmful software program written intentionally to enter a computer without the user's permission or knowledge. It has the ability to replicate itself, thus continuing to spread. Some viruses do little but replicate, while others can cause severe harm or affect the program and performance of the system.
2 How Do I Know I’ve Got Virus in My Computer?
You may not notice that your computer is under attack until you realize something is missing or wrong when you open an attachment or a program with virus. Here is couple of signs which may show you that your computer is under attack.
• Your computer work slower than it was.
• Your computer freezes frequently or doesn’t open properly
• Your computer restarts in every couple minutes.
• Your system doesn’t work properly and restarts itself
• Applications in your computers don’t work properly.
• You cannot reach to discs and drivers
• You cannot print
• You are seeing unusual errors
• You see messed up-shaped menus
There are number of computer viruses that can impede the functioning of your computer system. Computer viruses usually spread in one of three ways:
from removable media;
from downloads off the Internet; and
from e-mail attachments.
Although the Internet gets a bad rap as a source of viruses, you're no more likely to contract a virus from the Web than you are from packaged software. Still, scan everything you download, and update your antivirus software regularly.
Why Do People Create Computer Viruses?
-To take control of a computer and use it for specific tasks
-To generate money
-To steal sensitive information (credit card numbers, passwords, personal details, data etc.)
-To prove a point, to prove it can be done, to prove ones skill or for revenge purposes
-To cripple a computer or network
Types of Computer Viruses
1. Memory Resident Virus
Ø These viruses fix themselves in the computer memory and get activated whenever the OS runs and infects all the files that are then opened.
Ø This type of virus hides in the RAM and stays there even after the malicious code is executed. It gets control over the system memory and allocate memory blocks through which it runs its own code, and executes the code when any function is executed.
Ø Examples: Randex, CMJ, Meve, and MrKlunky .
Ø This type of virus affects the boot sector of a hard disk. This is a crucial part of the disk, in which information of the disk itself is stored along with a program that makes it possible to boot (start) the computer from the disk. This type of virus is also called Master Boot Sector Virus or Master Boot Record Virus.
Ø It hides in the memory until DOS accesses the floppy disk, and whichever boot data is accessed, the virus infects it.
Ø Examples: Polyboot.B, AntiEXE
3. Macro Virus
Ø Macro viruses infect files that are created using certain applications or programs that contain macros, like .doc, .xls, .pps, .mdb, etc. These mini-programs make it possible to automate series of operations so that they are performed as a single action, thereby saving the user from having to carry them out one by one. These viruses automatically infect the file that contains macros, and also infects the templates and documents that the filecontains. It is referred to as a type of e-mail virus.
Ø These hide in documents that are shared via e-mail or networks.
Ø Examples: Relax, Melissa.A, Bablas, O97M/Y2K
4. Directory Virus
Ø Directory viruses (also called Cluster Virus/File System Virus) infect the directory of your computer by changing the path that indicates the location of a file. When you execute a program file with an extension .EXE or .COM that has been infected by a virus, you are unknowingly running the virus program, while the original file and program is previously moved by the virus. Once infected, it becomes impossible to locate the original files.
Ø It is usually located in only one location of the disk, but infects the entire program in the directory.
Ø Examples: Dir-2 virus
Ø Polymorphic viruses encrypt or encode themselves in a different way (using different algorithms and encryption keys) every time they infect a system. This makes it impossible for antivirus software to find them using string or signature searches (because they are different in each encryption). The virus then goes on to create a large number of copies.
Ø Examples: Elkern, Marburg, Satan Bug and Tuareg
Ø The file allocation table (FAT) is the part of a disk used to store all the information about the location of files, available space, unusable space, etc.
Ø FAT virus attacks the FAT section and may damage crucial information. It can be especially dangerous as it prevents access to certain sections of the disk where important files are stored.
Damage caused can result in loss of information from individual files or even entire directories.
Ø Examples: Link Virus
7. Web Scripting Virus Ø Many web pages include complex codes in order to create an interesting and interactive content. This code is often exploited to bring about certain undesirable actions.
Ø The main sources of web scripting viruses are the web browsers or infected web pages.
Ø Examples: JS.Fortnight is a virus that spreads through malicious e-mails.
. Worms
Ø A worm is a program very similar to a virus; it has the ability to self-replicate and can lead to negative effects on your system. But they can be detected and eliminated by antivirus software.
Ø These generally spread through e-mails and networks. They do not infect files or damage them, but they replicate so fast that the entire network may collapse.
Ø Examples: PSWBugbear.B, Lovgate.F, Trile.C, Sobig.D, Mapson
Trojans
Ø Another unsavory breed of malicious code are Trojans or Trojan horses, which unlike viruses, do not reproduce by infecting other files, nor do they self-replicate like worms. In fact, it is a program which disguises itself as a useful program or application.
Ø These viruses copy files in your computer (when their carrier program is executed) that can damage your data, and even delete it. The attacker can also program the trojans in such a manner that the information in your computer is accessible to them.
Ø Examples: Trojan.Vundo
Disadvantages oF Viruses
Ø Format hard disk
Ø Copy, rename and delete files
Ø Modify files dates and extensions
Ø Display false message every few times
Ø Damage data
Ø Damage software
-Computer runs slowly
Ø Random restarts
Ø Unknown and uninstalled icons on desktop
Ø Icons change in appearance
Ø System memory and disk space is reduced
Ø New windows open up at an alarming rate
Ø Error messages on regular basis
Ø Files mysteriously disappear
Computer Anti-Virus
Antivirus software is a computer program that detects, prevents, and takes action to disarm or remove malicious software programs, such as viruses and worms.
There are certain types of anti-viruses.
Best Computer Anti-Viruses
There are so many anti-viruses which works against viruses but some anti-viruses are trusted and are very famous.
Ø There are some most ranked anti-viruses
• Avira Antivirus
• Avast Antivirus
• AVG Antivirus
• Immunet Protect
• Emsisoft Antimalware
• Digital Patrol
• K7 Antivirus
• eScan Antivirus
• Comodo Antivirus
• Dr.Web Antivirus
• Digital Defender Antivirus
• Norman Antivirus
• Clam Antivirus
• Kaspersky
Advantages of Anti-Virus
---Protecting Personal Information
--- A good anti-virus program will protect you while you surf the Internet,
---preventing hackers from gaining access to personal things such as credit card information and bank account access. The firewall feature included with most antivirus.
---Antivirus software will block any unauthorized incoming connections to your network or computer, preventing hackers from digging their hooks into your life and your computer.
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