Computer viruses pose a very real threat to this technological age. As our dependence on computers increases so does the incidence of computer virus infection. Like their biological counterparts, complete eradication is virtually impossible. Thus all computer viruses which have been injected into the public domain still exist. This coupled with the fact that new viruses are being discovered every day is resulting in a massive escalation of computer virus incidence. Computer viruses covertly enter the system and systematically take control, corrupt and destroy. New viruses appear each day that circumvent current means of detection, entering the most secure of systems. Anti-Virus software writers find themselves fighting a battle they cannot win: for every hole that is plugged, another leak appears. Presented in this thesis is both method and apparatus for an Anti-Virus System which provides a solution to this serious problem. It prevents the corruption, or destruction of data, by a computer virus or other hostile program, within a computer system. The Anti-Virus System explained in this thesis will guarantee system integrity and virus containment for any given system. Unlike other anti-virus techniques, security can be guaranteed, as at no point can a virus circumvent, or corrupt the action of the Anti-Virus System presented. It requires no hardware modification of the computer or the hard disk, nor software modification of the computer's operating system. Whilst being largely transparent to the user, the System guarantees total protection against the spread of current and future viruses.