Securing a MongoDB deployment in AWS requires configuring security groups, including inbound firewall rules that limit access to trusted connections only, and granting SSH access to specific IP ranges for Cloud Manager agents. Allowing outgoing HTTPS traffic on port 443 is also crucial for agent communication. Additionally, using Cloud Manager's built-in features such as user authentication, SSL encryption, and monitoring and alerting systems can help reduce the attack surface and protect data from unauthorized access. By following best practices and leveraging Cloud Manager's automation capabilities, organizations can simplify security configuration and improve their overall security posture.