Network computing systems may implement data loss prevention (DLP) techniques to reduce or prevent unauthorized use or transmission of confidential information or to implement information controls mandated by statute, regulation, or industry standard. Implementations of network data transmission analysis systems and methods are disclosed that can use contextual information in a DLP policy to monitor data transmitted via the network. The contextual information may include information based on a network user's organizational structure or services or network infrastructure. Some implementations may detect bank card information in network data transmissions. Some of the systems and methods may be implemented on a virtual network overlaid on one or more intermediate physical networks that are used as a substrate network.