Malicious ip warnings

I know that a majority of the time it could be bots probing open ports when hosting multiplayer, but why do malicious ips flag even when in singleplayer. My ISP picks up traffic regardless if im in single or multiplayer. I would assume that this shouldnt even be happening at all if terraria/tmodloader runs on a private ip when doing an invite only multiplayer world, is this a unfixable thing or is there a solution?
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