Block user sign-in in Microsoft 365 Lighthouse
You can block a user account if you think it's compromised. When you block a user account, it immediately blocks anyone from signing in to that account. If a user tries to sign in, they're automatically signed out of all Microsoft 365 services within 60 minutes. Blocking a user account won't delete any data, and it won't stop the account from receiving mail.
Block sign-in for a user
In the left navigation pane in Lighthouse, select Users > Account management >Search users.
On the Search users tab, enter a user's name in the search box.
From the search results list, select the user.
In the user details pane, select Block sign-in.
In the Block sign-in pane, select Block this user from signing in.
Select Save changes.
Block sign-in for risky users
In the left navigation pane in Lighthouse, select Users > Risky users.
On the Risky Users page, select the set of users you want to take action on.
Select Block sign-in.
In the Manage sign-in status pane, select Block users from signing in.
Submit and view feedback for