Immutability for Azure SQL Database LTR backups

Hi

I was reading this Azure Update:
https://azure.microsoft.com/en-us/updates?id=523095

It says: [...] mitigating any potential ransomware attacks for the entire retention. 

My understanding is these backups are managed and stored by Microsoft. Does it mean that they are at risk of ransomware? If yes, does it mean that the entire estate in Azure is at risk of ransomware (e.g. Storage Accounts, etc.)

Thank you