Computer Viruses, Worms, and Trojans

In this article I describe Computer Viruses Worms and Trojans.

 A virus is a self-replicating program that uses other files or code to replicate. Most viruses infect files so that every time the host file is executed, the virus is executed too. Viruses can infect program files, boot sectors, hard drive partition tables, data files, memory, macro routines, and scripting files. Some viruses are very powerful, but even a powerful viruses cannot break hard drive read-write heads, or any physical device.

A Non-Resident Virus execute, does its damage, and terminates until the next time it is executed it is known as a nonresident virus.

A Memory-Resident Virus stay stays in memory after it is executed. Memory-resident viruses insert themselves as part of the operating system or application and can manipulate any file that is executed, copied, moved, or listed.

A virus that overwrites the host code with its own code, effectively destroying much of the original contents, it is called an overwriting virus

 The code that modified by virus dose not have to be a file, it can be a disk boot sector or partition table, in which case the virus is called a Boot Sector or Partition Table virus. If you see a error “Non-system disk” its mean boot sector virus attack on your PC. Most boot sector virus damage routines run at the beginning of the virus’s execution, before Windows is loaded. The virus can damage Windows by preventing it from loading or by formatting the hard drive. Boot sector viruses were very popular, and viruses like Stoned, Brain, Anti-Exe, Anti-CMOS, NYB, and Joshi spread around the world.

Macro viruses infect the data running on top of an application by using the program’s macro or scripting language. Macro virus was released in July 1995, it quickly launched a new extended wave of malicious code. Concept used Word document macros to propagate itself. It infected the Word global template, which is used as the blank document for all new documents.

In my next article about virus I will discuss the virus that attack on Android base system i.e tablets and Smart phones.

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