This paper is an attempt to summarize why exactly the general public appreciates computer viruses as something inherently bad. It is also considering several of the proposed models of "beneficial" viruses and points out the problems in them. A set of conditions is listed, which every virus that claims to be beneficial must conform to. At last, a realistic model using replication techniques for beneficial purposes is proposed and directions are given in which this technique can be improved further.
An older, yet still very applicable essay on the merits and faults of writing 'good' viruses. As well as both good and bad examples of such attempts.