The document discusses 5 of the most costly network security threats faced by enterprises: 1) botnets, 2) phishing, 3) malware, 4) distributed denial of service (DDoS) attacks, and 5) increasingly sophisticated attacks. It recommends implementing key layers of control through network perimeter protections, cloud-based security services, mobile device security, and endpoint compliance to effectively prevent and mitigate these threats. Outsourcing security functions to a managed security services provider can help organizations do more with less by avoiding in-house technology and staffing costs.