Software systems in which many user's or programmers intervene may eas
ily contain software items - such as viruses - which will endanger the
integrity of the system. This paper proposes that in addition to the
conventional recovery techniques, such as dumps and roll-back recovery
, system availability be enhanced by the introduction of virus tests o
r other types of ''failure tests''. We present a model to analyze the
effect of the failure rate, the frequency of virus and failure testing
, and the frequency of periodic dumps, on global system availability.
We assume that the ''failure'' rate of the system increases as time el
apses beyond any individual instant at which a virus test or failure t
est has been carried out. Thus, we are dealing with a system in which
failures will be naturally time-dependent. We compute the optimum valu
e of the interval between dumps, and also the best time interval betwe
en virus or failure tests for this system. In order to illustrate the
methodology of this work, numerical examples are presented for various
time-dependent failure statistics.