WWII provides some interesting data points. On the one hand, yes, as Germany occupied numerous neighbours people - even sometimes in the face of group punishment, kept sabotaging the German military and its logistics. In some cases there are literally enemy agents, the Special Operations Executive† but often they're local partisans either working with the SOE or on their own.

But on the other hand, even though the Americans suspected that people who merely looked Japanese might be traitors, AFAIK there aren't any clear examples where the people who were sent to camps actually were enemy spies who'd have sabotaged America given the chance. And in Britain the counter-intelligence operation was so successful that when captured German spymasters revealed their list of agents in Britain, every name was already either working for Twenty Department (20 = XX = Double Cross, we can't resist a pun) or in prison for espionage or dead.

† notably in WWII if as a woman you say you want to be on a ship of the line, or crew front line aircraft and attack the Nazis you will be told women can't serve front line roles and at most you'll be doing delivery runs in relative safety. But if you know the right people to become a spy they will cheerfully send you behind enemy lines even though if caught you will almost certainly be horribly tortured and then probably killed and the government which sent you won't even acknowledge you existed for years.

So, maybe the risk from people who are already where your infrastructure is is much lower that you'd think if you haven't invaded them and occupied their land. On the other hand remote adversaries are definitely always a risk.