Viruses have the potential to infect any type of executable code, not just the files that are commonly called 'program files. For example, some viruses infect executable code in the boot sector of floppy disks or in system areas of hard drives. Another type of virus, known as a 'macro virus', can infect word processing and spreadsheet documents that use macros. And it's possible for HTML documents containing JavaScript or other types of executable code to spread viruses or other malicious code.

Since virus code must be executed to have any effect, files that the computer treats as pure data are safe. This includes graphics and sound files such as .gif, .jpg, .mp3, .wav, etc., as well as plain text files. For example, just viewing picture files won't infect your computer with a virus. The virus code has to be in a form, such as an exe program file or Word .doc file, that the computer will actually try to execute.

How do viruses spread?

LAN VIRUS: When you execute program code that's infected by a virus, the virus code will also run and try to infect other programs, either on the same computer or on other computers connected to it over a network. When you share a copy of an infected file with other computer users, running the file may also infect their computers; and files from those computers may spread the infection to yet more computers and creating network congestion (jam) on LAN as well as WAN (Internet Connection), which means other sites might also get inffected.

Since viruses are deliberately designed to damage files or otherwise interfere with your computer's operation, while others don't do anything but try to spread themselves around. But even the ones that just spread themselves are harmful, since they damage files and may cause other programs in the process of speading and can affect performance of your systems/LAN.

Contribution: J. Darwin, ARIS Cell, DRS, IGAU, Raipur