Abstract: Described are methods and apparatus, including computer program products, for propagation protection within a network. A transparent network appliance monitors data being transmitted from a first portion of the network to a second portion of the network through the network appliance and analyzes the data to determine whether the data represents a threat to the network. The network appliance transmits the data to the second portion of the network if the data does not represent a threat to the network or prevents transmission of the data to the second portion of the network if the data represents a threat to the network.