What does _HIDDEN_DUE_TO_SECURITY_REASONS_ mean in an ArcGIS Online activity log

When viewing the activity log downloaded from the Overview tab in the Organization page of ArcGIS Online, the message "HIDDEN_DUE_TO_SECURITY_REASONS" can sometimes be found in the id and actor columns.

When there is a failed login, either through a user name or password that does not exist in the organization, the user name is hidden. Since failed logins can also occur when a user name is incorrectly entered as the password or vice versa, the credentials must be hidden to prevent them from being revealed in the activity log. This ensures user names and passwords are only stored in the identity provider.