 Several worms, including some XSS worms, have been written to research how worms spread, such as the effects of changes in social activity or user behavior.One study proposed what seems to be the first computer worm that operates on the second layer of the OSI model (Data link Layer), utilizing topology information such as Content-addressable memory (CAM) tables and Spanning Tree information stored in switches to propagate and probe for vulnerable nodes until the enterprise network is covered.Anti-worms have been used to combat the effects of the Code Red, Blaster, and Santy worms.