Control "public connectivity to Free Microsoft Teams
Skype for Business Online allows administrators to control "public IM connectivity" on the admin portal.
Microsoft Teams also should allow administrators to control "public connectivity to free Microsoft Teams" on the admin portal.
O365 users worry that home users can install free Microsoft Teams on thier PCs and invite O365 users to their teams.
O365 users are more likeiy to wrongly upload confidential information to the free teams.