This document proposes NICE, a framework for secure intrusion detection and attack mitigation in virtual network systems. NICE uses distributed agents on cloud servers to monitor traffic, detect vulnerabilities, and generate attack graphs. It profiles virtual machines to identify their state and vulnerabilities. When potential attacks are detected, NICE can quarantine suspicious VMs and inspect their traffic. The attack analyzer correlates alerts, constructs attack graphs, and selects appropriate countermeasures based on the graphs. Evaluations show NICE can effectively detect attacks while minimizing performance overhead for the cloud system.