Unless he knows personal information about you like email address, password, Date of birth etc then he is very unlikely to be able to hack you.
He could do a denial of service attack where you floods your IP address with useless traffic kicking you offline.
If he does do it then you just need to change your public IP address. This can usually be done by switching off your modem/router for a few minutes. After switching back on you will have a new public IP address and unless you play against him again he wont
be able to attack you.
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