In this article, i will write about, what is the virus? What adverse effects the virus on your computer or laptop? How does the virus work? The answer to that question i mentioned it in this article.
A virus reproduces, usually without your permission or knowledge. In general terms they have an infection phase where they reproduce widely and an attack phase where they do whatever damage they are programmed to do (if any). There are a large number of virus types. Viruses are a cause of much confusion and a target of considerable misinformation even from some virus "experts."
Let's define what we mean by virus:
A virus is a program that reproduces its own code by attaching
itself to other executable files in such a way that the virus code is
executed when the infected executable file is executed.
You could probably also say that the virus must do this without the permission or knowledge of the user, but that's not a vital distinction for purposes of our discussion here. We are using a broad definition of "executable file" and "attach" here.
An obvious example of an executable file would be a program (COM or EXE file) or an overlay
or library file used by an EXE file. Less obvious, but just as critical, would be the macro portion of what you might generally consider to be a data file (e.g., a Microsoft Word document). It's important to also realize that the system sectors on either a hard or floppy disk contain executable code that can be infected--even those on a data disk. More recently, scripts written for internet web sites and/or included in E-mail can also be executed and infected. To attach might mean physically adding to the end of a file, inserting into the middle of a file, or simply placing a pointer to a different location on the disk somewhere where the virus can find it.
Most viruses do their "job" by placing self-replicating code in other programs, so that when those other programs are executed, even more programs are "infected" with the self-replicating code. This self-replicating code, when triggered by some event, may do a potentially harmful act to your computer.
Another way of looking at viruses is to consider them to be programs written to create copies of themselves. These programs attach these copies onto host programs (infecting these programs). When one of these hosts is executed, the virus code (which was attached to the host) executes, and links copies of itself to even more hosts. Similar to viruses, you can also find malicious code in Trojan Horses, worms, and logic bombs.
Often the characteristics of both a virus and a worm can be found in the same beast; confusing the issue even further.
Virus Behaviour
Infect, then attack; common behavior of most viruses.
Number of Viruses
Lots and lots.
How Serious Are Viruses?
Worms spreading due to user inattention are a serious threat.
What About Good Viruses?
The general consensus is that there are none.
Hardware Threats
Viruses are not the only things that can cause damage. Consider some hardware problems.
Software Threats
Viruses are not the only things that can cause damage. Consider some software problems.
Virus Types
Viruses come in many types; written using many different infection strategies.
Viruses come in a variety of types. Breaking them into categories is not easy as many viruses
have multiple characteristics and so would fall into multiple categories. We're going to describe two different types of category systems: what they infect and how they infect. Because they are so common, we're also going to include a category specific to worms.
What They Infect
These categories include:
System Sector Viruses,These infect control information on the disk itself.
File Viruses,These infect program (COM and EXE) files.
Macro Viruses,These infect files you might think of as data files. But, because they contain macro programs they can be infected.
Companion Viruses,A special type that adds files that run first to your disk.
Cluster Viruses,A special type that infects through the disk directory.
Batch File Viruses,These use text batch files to infect.
Source Code Viruses,These add code to actual program source code.
Visual Basic Worms,These worms use the VisualBasic language to control the computer and perform tasks.
How They Infect
Viruses are sometimes also categorized by how they infect. These categorizations often
overlap the categories above and may even be included in the description (e.g., polymorphic
file virus). These categories include:
Polymorphic Viruses,Viruses that change their characteristics as they infect.
Stealth Viruses,Viruses that try to actively hide themselves from anti-virus or system software.
Fast and Slow Infectors,Viruses that infect in a particular way to try to avoid specific anti-virus software.
Sparse Infectors,Viruses that don't infect very often.
Armored Viruses,Viruses that are programmed to make disassembly difficult.
Multipartite Viruses,Viruses that may fall into more than one of the top classes.
Cavity (Spacefiller) Viruses,Viruses that attempt to maintain a constant file size when infecting.
Tunneling Viruses,Viruses that try to "tunnel" under anti-virus software while infecting.
Camouflage Viruses,Viruses that attempted to appear as a benign program to scanners.
NTFS ADS Viruses,Viruses that ride on the alternate data streams in the NT File System.
And, in a special category, one might include Virus Droppers,Programs that place vises onto your system but themselves may not be viruses (a special form of Trojan).
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