How can i tell if someone has logged into my account

OnStar and General Motors take matters that affect our members' safety and security very seriously, Mario. GM maintains appropriate security standards, practices, guidelines and controls aimed at defending the vehicle and the vehicle service ecosystem against unauthorized electronic access, detecting possible malicious activity in related networks, and responding to suspected cyber security incidents in a timely, coordinated and effective manner. Can you explain specifically what happened for you to believe that your account was compromised?  Please send an email to socialmedia@gm.com with this information for further assistance. Also, please make sure to put "ATTN: OS Community/Marionoble," in the subject line so that we can locate your message. Our team will keep an eye out for your response.