The most effective course of action when employees are using free cloud storage services to store company data through their mobile devices is to assess the business need to provide a secure solution, such as a corporate-approved cloud service or a virtual desktop environment. Assessing the business need can help understand why employees are using free cloud storage services, what kind of data they are storing, and what are the security risks and requirements. Based on the assessment, the security manager can propose a secure solution that meets the business needs and complies with the BYOD policy. The other options, such as allowing the practice to continue, disabling remote access, or initiating remote wipe, may not address the underlying business need or may cause disruption or data loss. References:

https://www.digitalguardian.com/blog/byod-security-expert-tips-policy-mitigating-risks-preventing-breach

https://news.microsoft.com/en-xm/2021/03/18/how-to-have-secure-remote-working-with-a-byod-policy/

https://www.trendmicro.com/vinfo/us/security/news/cybercrime-and-digital-threats/-infosec-guide-bring-your-own-device-byod