What happens when someone logs into your Facebook account?

Answer 1

When someone either inadvertently or deliberately logs into your Facebook account, a few things could happen. They can see everything about your account because they are logged in as you. This means they can see (and subsequently change) your account settings, your inbox, they can post messages and fb posts as you...the whole nine yards. If this person's intent is malicious i.e. your account has been hacked, they may change your password, make changes to your profile, send out messages that contain spam or viruses, etc. If the person has logged onto your account as a way of playing a joke or something of that nature, the 'damage' will probably be minimal and more embarrassing than anything.

Also, if your account is hacked from half way across the country or half way across the world and you attempt to access your account at the same time as the hacker, you may get a message alerting you that your account has been hacked. You will then have to answer a few security questions. As long as the questions are answered properly, you should regain access to your account.