Computer virus
computer virus is a type of malicious software program ("malware") that, when executed, replicates by reproducing itself (copying its own source code) by infecting other computer programs by modifying them.[1] Infecting computer programs can include as well, data files, or the "boot" sector of the hard drive. When this replication succeeds, the affected areas are then said to be "infected" with a computer virusr virus
Computer viruses currently cause billions of dollars' worth of economic damage each year
Once a virus has successfully attached to a program, file, or document, the virus will lie dormant until circumstances cause the computer or device to execute its code. In order for a virus to infect your computer, you have to run the infected program, which in turn causes the virus code to be executed. This means that a virus can remain dormant on your computer, without showing major sings or symptoms. However, once the virus infects your computer, the virus can infect other computers on the same network. Stealing passwords or data, logging keystrokes, corrupting files, spamming your email contacts, and even taking over your machine are just some of the devastating and irritating things a virus can do.
TYPE OF Computer virus
Most Common Types of Viruses and Other Malicious Programs
1. Resident Viruses
This type of virus is a permanent which dwells in the RAM memory. From there it can overcome and interrupt all of the operations executed by the system: corrupting files and programs that are opened, closed, copied, renamed etc.
Examples include: Randex, CMJ, Meve, and MrKlunky.
2. Multipartite Viruses
Multipartite viruses are distributed
through infected media and usually hide in the memory. Gradually, the
virus moves to the boot sector of the hard drive and infects executable
files on the hard drive and later across the computer system.
3. Direct Action Viruses
The main purpose of this virus is to replicate and take action when it is executed. When a specific condition is met, the virus will go into action and infect files in the directory or folder that it is in and in directories that are specified in the AUTOEXEC.BAT file PATH. This batch file is always located in the root directory of the hard disk and carries out certain operations when the computer is booted.
4. Overwrite Viruses
Virus of this kind is characterized by the fact that it deletes the information contained in the files that it infects, rendering them partially or totally useless once they have been infected.
The only way to clean a file infected by an overwrite virus is to delete the file completely, thus losing the original content.
Examples of this virus include: Way, Trj.Reboot, Trivial.88.D.
5. Boot Virus
This type of virus affects the boot sector of a floppy or hard disk. This is a crucial part of a disk, in which information on the disk itself is stored together with a program that makes it possible to boot (start) the computer from the disk.
The best way of avoiding boot viruses is to ensure that floppy disks are write-protected and never start your computer with an unknown floppy disk in the disk drive.
Examples of boot viruses include: Polyboot.B, AntiEXE.
6. Macro Virus
Macro viruses infect files that are created using certain applications or programs that contain macros. 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.
Examples of macro viruses: Relax, Melissa.A, Bablas, O97M/Y2K.
7. Directory Virus
Directory viruses change the paths that indicate the location of a file. By executing a program (file with the extension .EXE or .COM) which has been infected by a virus, you are unknowingly running the virus program, while the original file and program have been previously moved by the virus.
Once infected it becomes impossible to locate the original files.
8. Polymorphic Virus
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 anti-viruses to find them using string or signature searches (because they are different in each encryption) and also enables them to create a large number of copies of themselves.
Examples include: Elkern, Marburg, Satan Bug, and Tuareg.
9. File Infectors
This type of virus infects programs or executable files (files with an .EXE or .COM extension). When one of these programs is run, directly or indirectly, the virus is activated, producing the damaging effects it is programmed to carry out. The majority of existing viruses belongs to this category, and can be classified depending on the actions that they carry out.
10. Encrypted Viruses
This type of viruses consists of
encrypted malicious code, decrypted module. The viruses use encrypted
code technique which make antivirus software hardly to detect them. The
antivirus program usually can detect this type of viruses when they try
spread by decrypted themselves.
11. Companion Viruses
11. Companion Viruses
Companion viruses can be considered file infector viruses like resident or direct action types. They are known as companion viruses because once they get into the system they "accompany" the other files that already exist. In other words, in order to carry out their infection routines, companion viruses can wait in memory until a program is run (resident viruses) or act immediately by making copies of themselves (direct action viruses).
Some examples include: Stator, Asimov.1539, and Terrax.1069
12. Network Virus
Network viruses rapidly spread
through a Local Network Area (LAN), and sometimes throughout the
internet. Generally, network viruses multiply through shared resources,
i.e., shared drives and folders. When the virus infects a computer, it
searches through the network to attack its new potential prey. When the
virus finishes infecting that computer, it moves on to the next and the
cycle repeats itself.
The most dangerous network viruses are Nimda and SQLSlammer.
13. Nonresident Viruses
This type of viruses is similar to
Resident Viruses by using replication of module. Besides that,
Nonresident Viruses role as finder module which can infect to files when
it found one (it will select one or more files to infect each time the
module is executed).
14. Stealth Viruses
Stealth Viruses is some sort of
viruses which try to trick anti-virus software by intercepting its
requests to the operating system. It has ability to hide itself from
some antivirus software programs. Therefore, some antivirus program
cannot detect them.
15. Sparse Infectors
In order to spread widely, a virus
must attempt to avoid detection. To minimize the probability of its
being discovered a virus could use any number of different techniques.
It might, for example, only infect every 20th time a file is executed;
it might only infect files whose lengths are within narrowly defined
ranges or whose names begin with letters in a certain range of the
alphabet. There are many other possibilities.
16. Spacefiller (Cavity) Viruses
Many viruses take the easy way out
when infecting files; they simply attach themselves to the end of the
file and then change the start of the program so that it first points to
the virus and then to the actual program code. Many viruses that do
this also implement some stealth techniques so you don't see the
increase in file length when the virus is active in memory.
A spacefiller (cavity) virus, on the other
hand, attempts to be clever. Some program files, for a variety of
reasons, have empty space inside of them. This empty space can be used
to house virus code. A spacefiller virus attempts to install itself in
this empty space while not damaging the actual program itself. An
advantage of this is that the virus then does not increase the length of
the program and can avoid the need for some stealth techniques. The
Lehigh virus was an early example of a spacefiller virus.
17. FAT Virus
The file allocation table or FAT is the part of a disk used to connect information and is a vital part of the normal functioning of the computer.
This type of virus attack can be especially dangerous, by preventing access to certain sections of the disk where important files are stored. Damage caused can result in information losses from individual files or even entire directories.
18. Worms
A worm is technically not a virus, but a program very similar to a virus; it has the ability to self-replicate, and can lead to negative effects on your system and most importantly they are detected and eliminated by antiviruses.
Examples of worms include: PSWBugbear.B, Lovgate.F, Trile.C, Sobig.D, Mapson.
19. Trojans or Trojan Horses
Another unsavory breed of malicious code (not a virus as well) are Trojans or Trojan horses, which unlike viruses do not reproduce by infecting other files, nor do they self-replicate like worms.
20. Logic Bombs
They are not considered viruses because they do not replicate. They are not even programs in their own right but rather camouflaged segments of other programs.
Their objective is to destroy data on the computer once certain conditions have been met. Logic bombs go undetected until launched, and the results can be destructive.
How to protect against computer viruses?
Instead, look into comprehensive security software like Norton Security.
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