This is the second time this message has been displayed. I have changed my password and then 24 hours later, Mojang resets my password again. Here is the text:
Due to recent suspicious activity in your account we suspect that your Mojang account email and password may have been compromised. To prevent unauthorized use of your account we've reset your account password. If you use that same password on other sites we strongly recommend that you change your password on those sites as well.
Messages like that are usually relating to other people trying to or actually accessing your account. I would change your password to a much stronger password, and if you are sharing your account with someone else, don't since that is a serious security issue and may be what is causing your problem.
You need to change the password of your connected e-mail account as well. Anyone with access to that account can regain access to your Mojang account. Also you should no longer give access to your Mojang account, if you did so in the past.
Of course you should change all passwords of the accounts connected to that e-mail account and all passwords that were equal to your stolen one.
