Tuesday, 31 July 2018

Virus - Types


Virus
A virus is programming code that is designed to cause damage and is disguised to appear to be a normal program. Most viruses are also designed to clone themselves if they find a network environment so that they can move on to the other computers. Almost all virus infections occur over the Internet, attached to e-mail, attached to a file that you download, or sent over an Instant Message connection.
Viruses can erase data, replace program files, and change system files. Some viruses cause enough damage to the operating system files to make it impossible to boot the computer, rendering the machine useless. Some viruses go to work as soon as you inadvertently start them, but other viruses are programmed to wait until certain circumstances cause their code to be executed. Viruses arrive in many categories, and within each category many subcategories exist. Following are the most common categories of virus.




File-infecting viruses:
File infectors are the oldest virus type. These viruses attach themselves to program files, which are usually files with the filename extension .com or .exe. When the program is loaded, the virus is loaded as well, and it does its work independent of the program that runs when you open the program file. The program file is just the mode of transportation the way the virus gets itself loaded into memory. Some viruses can also be programs at the same time. The filename is seems to harmless, and the filename extension is .exe. Opening the file unleashes the virus. This virus type is frequently transmitted to its victims as an e-mail attachment.
   
System and boot infectors:
System and boot infectors infect the code that’s placed in certain system areas on a drive. On a floppy disk, they attach themselves to the DOS boot sector. On hard drives, they attach themselves to the Master Boot Record (MBR). This virus type doesn’t launch itself into memory and go to work until the next time you boot your computer. If you boot using an infected disk the virus is activated. If you start your computer normally, the virus loads itself into system memory when the boot files on the MBR load. After it’s loaded into your system memory, the virus can control basic computer operations, and it can replicate itself to other drives on the computer or to other computers on the network. Some boot sector viruses are designed to destroy the computer’s ability to boot; others permit start up and then perform damaging processes all over the computer.

Macro viruses:
Macro viruses are usually programmed to do the same damage as file-infecting viruses, but they do not attach themselves to an executable file, nor as an executable file. Instead, they attach to a document and launch when the document is opened. Then they carry out their damaging agenda and replicate themselves into other documents. Macro viruses generally attach themselves to Visual Basic (VB) code, which some programs use to create or run Macros.

Trojan horses:
A Trojan horse performs the same malicious deeds that viruses perform, but Trojans doesn’t replicate themselves as virus. The main problem with Trojan horse is that it’s difficult to remove the damage it does, even after you catch and remove it. You may have to undo changes to the Registry, replace system files, or perform other manual tasks to rid your system of the damage done Trojans.
   
Worms:
A worm is always a self-contained program it never attaches to any other program. A worm must be opened manually. When opened it replicates itself. One characteristic of a worm is its ability to propagate itself across drives and computers that are connected via a network. Because they don’t attach to other programs they propagate easily and rapidly. Since they don’t need to a host file, they clone themselves anywhere including drives and drives of connected computers. Sometimes each clone that’s created carries a different assignment, so when all these copies leap into action, they can do the maximum amount of damage. Worms almost always arrive as e-mail attachments.

Virus hoaxes:
The threat of viruses is real problem to us, but dealing with virus hoaxes makes it worse. People who fall for these stupid hoaxes often end up damaging their systems by following the advice they receive. People fall for this stuff because they don’t have enough technical knowledge to recognize that most of the information doesn’t make sense

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