Our partner Oxygen Forensics, a cyber security expert, commented on the situation:
The easiest way to avoid security issues with various apps and other communication sources is to use a business phone not a personal one. Today it is uncommon to communicate with clients using a personal mailbox. Corporate mail is commonly used everywhere, but for some reason, a business phone is still a rare thing. However, it plays the same role for the company security - if an employee is dismissed, the mailbox and the phone number are withdrawn and blocked or transferred to another active member. Thus, the main risks are reduced, such as unintentional (as in this case) or deliberate leakage of the customer base to third parties, inappropriate communication with customers, and others. Besides, it is always better to use apps specially designed for businesses. For example, Whatsapp Business aimed for small and medium business communication with customers.