Do you use Planner with Teams? Are some of your teams private for reason? Are you a owner in the team? Then be careful when assigning tasks to someone. #TeamsTuesday
This is not a new issue, but often not thought about. When you work with a private team planner and there are tasks to be done you might assign a task to a responsible who is not a member of your team. The dialog says “Non-members” when you are adding a person so pay attention to that.
When you assign a task to non-member, they will be added to the team/group as member! That person can then participate in chat and gets access to read/edit files and notebooks just like any other member. And Planners too.
This adding to the group happens very easily unnoticed, so that’s why you have to be careful with this. I haven’t found another place yet, where you can add a person to a Team/Group this much unnoticed.
Eventually you get a message on team’s general channel that a person is added to the team, but there is a delay. First they are added to O365 Group members (access to SharePoint files and Planners), and after a delay that information is synced to Teams.
There is a user voice ticket about this, so if you want to make a difference: go ahead and vote.