If you are using Azure Platform, it is better to check your system if any vulnerability exists.
Azure is Microsoft's cloud based computing platform. It is similar to AWS. It can be used for IaaS, PaaS or SaaS. Some of the companies using Azure platform is LG Electronic, MSI Computer, and LinkedIn.
If you have any subdomains pointing to non-existing service, this situation may be abused by attackers. Attacker creates a page where victims will be redirected from the subdomain. This method may lead some information leakage of users.
Check your DNS records regularly to remove unused ones.