A multinational corporation has recently undergone a comprehensive digital transformation, moving most of its operations to cloud$-$based platforms. Which of the following represents the MOST critical cybersecurity concern in this scenario?

A$)$ Ensuring all employees have up$-$to$-$date antivirus software on their personal devices

B$)$ Implementing strong access control measures and encryption for data in transit and at rest

C$)$ Limiting the use of cloud services to reduce potential vulnerabilities

D$)$ Focusing solely on protecting against external threats to the cloud infrastructure