Difference with Security Groups in Office 365 admin portal and in Exchange management security enabled distribution group

Hi,

I'd like to know the difference with the Security groups (that are found on the left edge of Office 365 admin portal) and the Security enabled distribution groups (that are found on the Exchange management portal).

Reason why this came up is the rights management for Shared mailboxes.

ps. I know i can make those security enabled distribution groups and give rights to those for Shared mailboxes, but i'd like to know why those Security groups can't be added for that purpose.

Best regards,

Timi Rantanen