Jailbreak??

I would make sure your account is hidden in the privacy settings and then block the ones that are spamming you.

But is it jailbreaks or a app modified on pc in a bad way doing it?

No, it's simply a bot that is creating new bogus Microsoft accounts using new bogus e-mails. A Microsoft account includes a gamertag, which opens up the entire Xbox Live network of users. So it's nothing wrong with Xbox Live in that sense (nothing got hacked);
it's just a bot with a gamertag messaging every gamertag it can find before it gets blocked.

But is it jailbreaks or a app modified on pc in a bad way doing it?

Hello Master,

Sorry for the issue with bots. The best thing to do is report ignore and block them. There is nothing anyone can do here on the forums about this. Unfortunately, we are unable to get on your profile and see any information. You can check out the
Enforcement site under how do I to see what all you can do.

As Zero stated go to settings>account>privacy and online safety> Xbox live privacy>View details and customize>under communication and multiplayer>others can communicate with voice text invites select friends.

Thanks,

Brad

You can easily change settings to not get messages from non friends under your privacy settings. Reporting them is the correct thing to do.

Enforcement handles that. The forums/twitter/chat/support have no part in that part of the system so we can not help you here.

As for "Children" handing out credit card information that is on the heads of the owner of the credit card allowing such easy access to that info to be given out.