The best-known type of malware is probably the virus; although many pieces of malware are called viruses, they are nothing of the sort.
A virus is a piece of software that has been written to insert copies of itself into applications and data and onto crucial parts of a computer’s hard disk. Viruses are said to be self-replicating programs and date back as far as the early 1970s, but they only became well known with the advent of microcomputers and later, the internet.
Viruses attach themselves to specific applications on a computer and are activated when the program is first run. At that point, the virus may make a copy of itself on the hard disk and continue to run, or it may only run each time the application is used. Early viruses, relying on floppy disks for transmission, spread quickly as infected data disks were shared around an office, or pirated software was passed around a playground. Nowadays, viruses rely on devices such as flash memory cards or are transmitted through internet connections.
Although some viruses are not intended to cause harm, the majority of these programs are designed to harm users, by corrupting their data or attacking the operating system itself or providing an exploitable ‘back door’, giving attackers access to the computer. Even where no harm is intended, viruses consume memory, disk space and processing power.