A method comprising the steps of: monitoring, by a computer system, messages (301, 302) transmitted via a network for presence of pre-selected data according to a data protection policy, the pre-selected data being from a source having a tabular structure organized as columns and rows; only upon determining, by the computer system, that a header of an original message transmitted by a sender via the network indicates that the original message is to be searched for pre-selected data, searching the original message for data fragments that match elements of the pre-selected data from one or more random rows within the tabular structure of the source, the pre-selected data comprising security-sensitive information to be protected from being transmitted via the network, wherein said searching comprises: searching for groups with tuples in any order in a plurality of columns of the tabular structure that match the pre-selected data (656, 660); combining matching tuple sets by row numbers into groups; if a number of groups found is equal to zero, determining a violation has not been detected (658, 662, 680); if a number of groups found is greater than zero, determining a violation has been detected (658, 662, 682); and preventing an unauthorized transmission of the original message comprising the pre-selected data to a recipient (902, 1108), responsive to determining a violation has been detected; and upon determining, by the computer system, that the header of the original message transmitted by the sender indicates that the original message is not to be searched, facilitating an authorized transmission of the original message to the recipient without searching the original message transmitted by the sender for the pre-selected data and regardless of the presence of the pre-selected data in the original message transmitted by the sender. monitoring, by a computer system, messages (301, 302) transmitted via a network for presence of pre-selected data according to a data protection policy, the pre-selected data being from a source having a tabular structure organized as columns and rows; only upon determining, by the computer system, that a header of an original message transmitted by a sender via the network indicates that the original message is to be searched for pre-selected data, searching the original message for data fragments that match elements of the pre-selected data from one or more random rows within the tabular structure of the source, the pre-selected data comprising security-sensitive information to be protected from being transmitted via the network, wherein said searching comprises: searching for groups with tuples in any order in a plurality of columns of the tabular structure that match the pre-selected data (656, 660); combining matching tuple sets by row numbers into groups; if a number of groups found is equal to zero, determining a violation has not been detected (658, 662, 680); if a number of groups found is greater than zero, determining a violation has been detected (658, 662, 682); and preventing an unauthorized transmission of the original message comprising the pre-selected data to a recipient (902, 1108), responsive to determining a violation has been detected; and searching for groups with tuples in any order in a plurality of columns of the tabular structure that match the pre-selected data (656, 660); combining matching tuple sets by row numbers into groups; if a number of groups found is equal to zero, determining a violation has not been detected (658, 662, 680); if a number of groups found is greater than zero, determining a violation has been detected (658, 662, 682); and preventing an unauthorized transmission of the original message comprising the pre-selected data to a recipient (902, 1108), responsive to determining a violation has been detected; and upon determining, by the computer system, that the header of the original message transmitted by the sender indicates that the original message is not to be searched, facilitating an authorized transmission of the original message to the recipient without searching the original message transmitted by the sender for the pre-selected data and regardless of the presence of the pre-selected data in the original message transmitted by the sender.