What is a virus?

When we talk about viruses in relation to computers and the internet, we mean a program that can create a copy of itself and spread to other connected computers. It is very similar to viral illnesses from which it takes its name: one person has an ‘infectious’ virus, the viral cells replicate and the virus spreads to other members of that original person’s family, friends or co-workers through close contact. In computers, the virus spreads by infecting files on a shared space like a network file system or by email, downloaded from the internet or from a removable medium like a USB stick, floppy disk, CD or DVD.