Did I over react....?

My brother was on the laptop on the administrator's account (which is basically my mom's but she uses the desktop) because he doesn't have an account of his own and when I went to go on my pword had been removed and he's obviously the one who had done it because he was on last and since he didn't have his own account and had to use the administrator he could access mine and the guest account, so he removed my pword which led me to believe he had been on so I told my mom and asked her to make him his own account and put a pword so he couldn't do it again, because he has no right to look at my account and he could have changed stuff, he said he wasn't on my account he just removed the password so I checked the history to make sure because he doesn't know how to delete it and he was telling the truth. Did I do the right thing because in a way it is an invasion of privacy.. the same reason I had a key lock put on a door when I got a job and started to make money and he stole $10 (he says he found it but I was missing $10 and my mom said there was no proof so he didn't get in trouble...