Secure mobile wireless ad-hoc networks are frequently described in the technical literature as highly-desired and feasible. However only few stable and scalable physical realizations of such MANETs were actually reported. In this paper, we describe SWAT (a secure wireless agent-based testbed), a physical network of handheld and stationary computing nodes that provide a practical industrial-strength MANET based on IEEE standard 802.11b and agent technology. The system, using HP iPAQ units and tablet PCs, implements secure group-based applications and allows for real-time user revocation. It integrates algorithms and techniques from several proposed software libraries, including CLIQUES, Spread and Secure Spread, SEM, IPSec, and EMAA.