The 'Azure AD Service Principal Enumeration' detection rule identifies potential reconnaissance activities against Azure Active Directory (AAD). It focuses on detecting instances where the Microsoft Graph API is used to enumerate 10 or more service principals in a tenant. This type of activity is commonly associated with tools used for enumerating Azure resources, such as AzureHound and ROADtools, which attackers may employ to gather information for privilege escalation or other malicious activities. The detection leverages Azure Monitor logs, specifically the MicrosoftGraphActivityLogs, which provide detailed records of API calls made against AAD. By setting a threshold of 10 service principals, the rule aims to catch suspicious enumeration activities while allowing for legitimate administrative behavior. Fine-tuning of the rule is recommended based on organizational activity to reduce false positives.