1. A method comprising: receiving, by a computer system, user input identifying tabular source data, the tabular source data representing data that has a tabular structure; receiving, by the computer system, user input specifying one or more columns in the tabular source data to define parameters of a search, wherein the one or more columns comprises data that is to be protected from being transmitted via a network; searching, by the computer system, a plurality of messages for presence of data that matches data in at least one of the specified columns within the tabular source data; and preventing, by the computer system, an unauthorized transmission of the data in at least one of the plurality of messages that matches the data in at least one of the specified columns, wherein preventing comprises at least one of blocking the unauthorized transmission of the at least one of the plurality of messages containing the data that matches the data in at least one of the specified columns, rerouting the at least one of the plurality of messages containing the data that matches the data in at least one of the specified columns to a destination other than an intended recipient, or intercepting the unauthorized transmission of the data in the at least one of the plurality of messages that matches the data in at least one of the specified columns to a recipient.