That still does not explain how people are getting onto your Minecraft server unauthorized though.
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One they need to know your ip if they are connecting externally through their router to your router.
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Two they are directly connecting to your lan through your Wan or wireless AC which means that your wireless is open and not secured or that they are hacking
There is no other ways around it because you said you never gave your ip to anyone except your kids friends or their parents. Basically if you feel that only trusted ppl have this information then you have been compromised in some way and these would be the only two ways that they can get to your game server.
-in the case of wan/wireless It could be your neighbors
-in the case of your actual physical external facing ip it could be the friends parents have compromised you in terms of telling someone else the information to your server ip
Either way its not making sense in this case we cannot just scan for random ip’s and hack someone on the other end of the internet. They have to connect to you or give you that information before hand for you to know it.
Like example any website you visit or game server is going to log all incoming ip’s they don’t just know that info. the same with people and computers they have to obtain that information prior. On the exact flip side i did not know the dns or named ip address of this website until i found it on google right or youtube or some forum right meaning that someone else told it to me that someone else could be a search engine or what ever.
yes we can just type some digits with the right amount of numbers and decimal places. But the fact is they know you have a minecraft server which mean they are hacking your wan or they know your external facing ip because someone told them it.