A von Neumann probe should be less of a challenge than faster than light travel, so I think a slow moving ship is more likely. https://en.wikipedia.org/wiki/Se

A von Neumann probe should be less of a challenge than faster than light travel, so I think a slow moving ship is more likely. https://en.wikipedia.org/wiki/Self-replicating_spacecraft https://en.wikipedia.org/wiki/Self-replicating_spacecraft