VIRUS – (1) an infective agent that typically consists of a nucleic acid molecule in a protein coat, is too small to be seen by light microscopy, and is able to multiply only within the living cells of a host: the hepatitis B virus. (2) a harmful or corrupting influence. (3) a computer virus – a piece of code which is capable of copying itself and typically has a detrimental effect, such as corrupting the system or destroying data.