The virus is a kind of software that attacks data and information, and it has the power to increase its number. When a virus enters the computer, it gradually increases the number and attacks the data stored there, and finally makes the computer unusable after infecting the entire device, for example, a booting virus attacks the booting sector of the hard disk. Stone, Vienna, CIH, Folder, Trojan horse, etc. are some most familiar viruses. If the ICT device is somehow infected with a virus, it gradually increases in number. If a virus-infected file enters a virus-free computer or ICT device through CD, pen drive or any other device, the virus takes hold in the memory where it stays even after closing the file after completing the work. In this way, a virus-free computer or ICT device is infected with the virus. The same thing happens when a virus-infected program or a piece of software is run. In this way, the virus taking a stand in the memory attacks other files and programs. Some viruses instantly infect all the existing files and programs, and some viruses infect only new programs and files. Thus, the virus deletes files and corrupts programs, and causes serious damage to the machine. In this way, a virus-free computer is gradually infected with a virus, and it may spread to other computers through the CDs being written in the infected machine, hard disc, and the Internet.
