What changed?
Self-replication began as a theoretical and experimental idea on early networked computers. Creeper is historically important as an early moving, self-replicating program, but it should not automatically be equated with the later malicious malware category.
How it spread / worked conceptually
An experimental program could move between connected systems in a small research environment. Reaper is remembered as an early defensive response concept: find the program, remove it, and return the system to a clean state.
Why it mattered
It established a lasting question for computing: when software can copy or move itself, who controls that behavior and how is it observed?
Representative historical examples
Creeper (early 1970s) is often cited in histories of networked self-replication. Reaper followed as a program intended to locate and remove Creeper.
What defenders learned
The response model was already recognizable: observe unexpected behavior, locate it, and clean it.
What changed next?
Self-replication would soon leave research networks and encounter a new distribution medium: removable disks.