I have it on good authority that the Earth is currently home to several time travelers from the future. We don’t know they’re here because they dress themselves in period clothing and they’ve printed up enough of our paper money to be able to blend in to their surroundings without raising too many questions.
The real question is how many of these time travelers are there around the globe? Thousands? Hundreds? One?
I assume they’re historians, and that their intentions are noble. But what of those miscreants who would abuse the time traveling system to further their own agendas? How many are here to influence the future rather than observe the past?
These are real questions that we someday may need to deal with.