A system to verify publication data at a host computer system, the system including: an interface module, integrated with the host computer system, to receive a communication, including the publication data, the publication data to be published via a network by the host computer system at a future time; a database, coupled to the host computer system, to store the publication data; and a processor-implemented security module comprising means for identifying a reference within the publication data to external data that is not included within the communication, the external data to be retrieved from a system external from the host computer system, and retrieved directly from the external system when the publication data is rendered by a client accessing the publication data over the network, the security module being characterized by: means for storing the reference and the external data as reference external data at the host computer system, means for repetitively retrieving, over a period of time spanning both before publication over the network and after initial publication over the network, the external data identified by the reference from the system external from the host computer system, means for, subsequently to each retrieval of the external data, comparing the retrieved external data against the reference external data to determine whether the external data has been modified to determine whether the external data is malicious, and preventing publication of the reference if the external data is malicious. an interface module, integrated with the host computer system, to receive a communication, including the publication data, the publication data to be published via a network by the host computer system at a future time; a database, coupled to the host computer system, to store the publication data; and a processor-implemented security module comprising means for identifying a reference within the publication data to external data that is not included within the communication, the external data to be retrieved from a system external from the host computer system, and retrieved directly from the external system when the publication data is rendered by a client accessing the publication data over the network, the security module being characterized by: means for storing the reference and the external data as reference external data at the host computer system, means for repetitively retrieving, over a period of time spanning both before publication over the network and after initial publication over the network, the external data identified by the reference from the system external from the host computer system, means for, subsequently to each retrieval of the external data, comparing the retrieved external data against the reference external data to determine whether the external data has been modified to determine whether the external data is malicious, and preventing publication of the reference if the external data is malicious. means for storing the reference and the external data as reference external data at the host computer system, means for repetitively retrieving, over a period of time spanning both before publication over the network and after initial publication over the network, the external data identified by the reference from the system external from the host computer system, means for, subsequently to each retrieval of the external data, comparing the retrieved external data against the reference external data to determine whether the external data has been modified to determine whether the external data is malicious, and preventing publication of the reference if the external data is malicious.