Then I do believe that the chances of your account being used by someone else without your consent is extremely low. Mojang's website had a temporary security breach and it affected migrated accounts.
Since yours wasn't migrated, your account is most likely not affected by this. Even then, we've had a 1 in 1,000 chance (roughly) of someone actually proving that their account was hacked by an outside source (a very small chance). If I were you, I'd make sure that you secure your account with a better password so that something like this doesn't happen again.
