The last thing you want to happen is when your (global) admin accounts are compromised. One easy way to avoid this is to enable multi factor authentication or MFA for you tenant admin accounts.
To achieve this, go to the Office 365 admin center and select the active users. Click More and select Multifactor Authentication setup as shown below:
You’ll see a list of all users in your organization that have MFA enabled. If this is the first time you’re here, most likely all users will have MFA set to disabled.
To show only the Global Administrators select Global Administrators in the View dropdown box. Select the Global Administrator and select Enable under Quick Steps.