Abstract: Systems, methods, and computer programming media useful in the identification and prevention of fraudulent activity on computer networks. In various aspects the invention provides methods, systems, and programming for monitoring requests received by network resources for access to data by remote signal sources. Signal source identifiers such as URLs associated with original and referred data requests are checked for satisfaction of one or more trustworthiness criteria. If the network identifier associated with the remote signal source does not satisfy the trustworthiness criteria, data associated with the untrusted signal source is assessed to determine whether it comprises fraudulent or suspicious content. If the data comprises fraudulent or suspicious content, the source of the data can be referred for further investigation or enforcement action, either by the operator or processor assessing the data, or by a network enforcement resource such as network standards or law enforcement agencies.