1. A method comprising: monitoring, by a computer system, messages transmitted via a network for presence of pre-selected data, the pre-selected data being from a source having a tabular structure; determining, by the computer system, that a message for transmission to a recipient via the network includes data fragments that match elements of the pre-selected data from at least one random row within the tabular structure of the source, the pre-selected data including security-sensitive information to be protected from being transmitted via the network; and preventing, by the computer system, an unauthorized transmission of the pre-selected data to the recipient to prevent loss of the security-sensitive information.