If he is going to hack your account etc, make your password extremely long, this makes it 100x harder to crack the account.
I think he only logged in, in offline mode. Anyone can do this with any account so you should be safe. Only if you see him login with your correct details you should be worried.
Oh, then you should be bleeping yourself right now!<3 just change the pass to like 100 letters / numbers / caps etc but write it down so u dont forget. Make sure to change all security questions and answers and your email so he cant do it again.
Good news, I just checked my login locations on my gmail and nobody has logged into my email from Russia or anywhere out of Maryland. YAY! So, this kid hasn't hacked my email yet. Therefore, he can't take my account from me.
I just made a fresh new email for Minecraft and changed my password to a long combination of letters and numbers.
Great update! I've changed my Mojang email and changed all of my passwords related to Minecraft to a combination of letters and numbers. I've also enabled 2-step-verification for all 3 of my gmail accounts, so if this kid tries to get in my email, he'll have to have my iPhone in his hand to get a code.