See SelfReplication

''There's a lot of useful content on the SelfReplication page. However, I have a question that relates specifically to SelfReplicatingSoftware. We all know about ''malicious'' self-replicating software (viruses, worms, etc.). But are there any extant examples of ''useful'' self-replicating software? I have heard it suggested that one could create an "anti-worm", a worm that traverses a network eliminating a malicious worm, but has this actually been done? And are there any other applications of beneficial self-replicating software?''