O365 manager Plus provides you User Logon Reports which help you detect unusual logon activities. Reports provided under this category include, User Logon Activity report, Recent Logon Failure report, and Recent Successful Logon Report.

To detect brute force attacks, you can make use of Recent Logon Failure Report, which lists you the recent failed login attempts, which is a clear sign of malicious activity when the number of attempts are high.

Recent Logon Failure Report

1. Go to Reports tab. 
2. In the left pane under Azure Active Directory, select User Report.
3. Under User Logon Reports, select Recent Logon Failure. [Refer image]

You can make use of filter option to retrieve only the required details. For example, you can get details based on duration, user, device used to login, and more. Schedule the reports to be generated automatically at regular intervals and export to PDF, XLS, HTML, or CSV format. You can also choose to email the report to the administrator.

Schedule Report

1. Select Admin tab.
2. In the left pane, select Administration --> Schedule report
3. Select Schedule new reports [Refer image]
4. Give a name for the scheduler, in Scheduler name field.
5. In Select Report field, select the report which you want to schedule. [Refer image]
6. Select the interval at which the report must be generated, and other required details in the subsequent fields.
7. Select Email this scheduled report, if you need to email this report to the administrator. [Refer image]
8. Select Message settings to configure message subject and body of the message. [Refer image]
9. Click Save. [Refer image]

To know more about the reports provided by O365 Manager Plus, click here