You can view a list of closed alerts and you can view the history of an individual closed alert to determine why it was closed.
To view a list of all closed alerts on the Alerts page:
From the main menu, select Investigate > Alerts.
Select Closed in the State column to filter the page to see only closed alerts.
To view the history of a closed alert:
From the main menu, select Investigate > Alerts.
Click on a closed alert in the alerts list to display the alert details.
Select the History tab for the closed alert. If a reason was given for closing the alert is can be seen on this tab. For more information, see Viewing alert revision history.