Network Data Loss Prevention (DLP) is the most effective strategy as it is specifically designed to address the core requirement: preventing sensitive data exfiltration. Network DLP solutions are deployed at network egress points to monitor, inspect, and control data in motion. They analyze the content of network traffic, including emails, web uploads, and cloud service interactions, against predefined policies. If a policy violation is detected (e.g., an attempt to send a file containing intellectual property), the DLP system can block the transmission, alert administrators, or apply encryption, directly preventing the unauthorized sharing of sensitive data.

A. Encryption protects data from unauthorized access during storage or transit but does not prevent an authorized user from decrypting and sharing the data.

B. Antivirus software is designed to detect and remove malware; it does not analyze or control the content of outbound data for policy violations.

C. Firewall rules manage network traffic based on ports, protocols, and IP addresses, but they lack the content-awareness needed to identify and block sensitive data.

1. Cloud Security Alliance (CSA). (2017). Security Guidance for Critical Areas of Focus in Cloud Computing v4.0. Page 67

Section "Data Loss Prevention (DLP)". The document states

"Network DLP... is typically installed at network egress points near the perimeter... It analyzes network traffic to detect sensitive data that is being sent in violation of information security policies."

2. National Institute of Standards and Technology (NIST). (2020). NIST Special Publication 800-53

Revision 5: Security and Privacy Controls for Information Systems and Organizations. Control ID SI-4 (18)

"Analyze Traffic | Content". This control enhancement specifies the need to "Analyze the content of network traffic to identify and position unauthorized information for removal." This directly supports the function of a Network DLP system.