A virus is a computer program that can copy itself and infect a computer without the user's permission or knowledge. There are 5 main types of viruses: macro, boot sector, network, logic bomb, and worm. An antivirus is a security program installed on a computer to protect it from viruses. Popular antivirus software includes K7, Kaspersky, Quickheal, and Avast Norton. A firewall protects a computer when connected to a network. Hackers break into computers to change data without permission, while crackers break in but do not change data. Freeware is free programming offered for download and use. An operating system acts as an interface between the user and computer, with examples including Windows XP, 7, 8,
