Detection and remediation of security incidents (e.g., attacks, compromised machines, policy violations) is an increasingly important task of system administrators. While numerous tools and techniques are available (e.g., Snort, nmap, netflow), novel attacks and low-grade events may still be hard to detect in a timely manner. In this paper, we present a novel approach for detecting stealthy, low-grade security incidents by utilizing information across a community of organizations (e.g., banking industry, energy generation and distribution industry, governmental organizations in a specific country, etc). The approach uses netflow, a commonly available non-intrusive data source, analyzes communication to/from the community, and alerts the community members when suspicious activity is detected. A community-based detection has the ability to detect incidents that would fall below local detection thresholds while maintaining the number of alerts at a manageable level for each day.