Complex sentence: The program rarely if ever actually replicated itself, rather it jumped from one system to another, attempting to remove itself from previous systems as it propagated forward, thus Creeper didn't install multiple instances of itself on several targets, it just moseyed around a network.
Split into simpler sentences: The program rarely if ever actually replicated itself; rather, it jumped from one system to another, attempting to remove itself from previous systems as it propagated forward. Thus, Creeper didn't install multiple instances of itself on several targets, it just moseyed around a network.