Microsoft on Thursday warned thousands of its cloud computing customers, including some of the world's largest companies, that intruders could have the ability to read, change or even delete their main databases, according to a copy of the email and a cyber security researcher.

The vulnerability is in Microsoft Azure's flagship Cosmos database. A research team at security company Wiz discovered it was able to access keys that control access to databases held by thousands of companies. Wiz Chief Technology Officer Ami Luttwak is a former chief technology officer at Microsoft's Cloud Security Group...