John Croall, Ian McKay
British Medical Journal, vol. 297, pp.981-982
ISSN 0959-8138
October 1988
Dr Patrick J R Harkin (10 September, p 688) doubts the hypothesis described by one of us (JC) (13 August, p 488) that computer viruses may evolve (and may already have evolved) by random substitution and cumulative selection from preexisting pieces of software.