1. A computer program product for dynamically de-identifying sensitive data from a data source for a target application, the computer program product comprising a computer readable storage device having computer readable program code embodied therewith, the computer readable program code being configured to cause a hardware processor to: generate a default rule set including at least one rule, the default rule set including a default de-identification protocol to produce de-identified data from an Extract/Transform/Load (ETL) tool, wherein the default de-identification protocol is selected based on business rules; map the default rule set to data definitions each generated by a discovery tool and associated with a corresponding sensitive data element identified in the data; specify a runtime rule set comprising at least one runtime rule, the runtime rule including a runtime de-identification protocol to produce de-identified data from the ETL tool, wherein the runtime rule set is specified via an interface; replace the default rule set with the runtime rule set to change the default de-identification protocol to the runtime de-identification protocol at runtime to accommodate changing de-identification requirements of a target environment, and map the runtime rule set to the data definitions, wherein each data definition includes a data object comprising metadata, including an indicator of a type of sensitive data from among a plurality of types of sensitive data and information indicating the location of the data element within the data source, for that data element, and each runtime rule is mapped to a corresponding data definition of a sensitive data element based on the type of sensitive data; and receive the data and the data definitions, and for each data definition: obtain the runtime rule mapped to that data definition; and apply the obtained runtime rule to the sensitive data element corresponding to that data definition in the received data and dynamically de-identify the sensitive data element for the target application by the ETL tool at runtime via the runtime de-identification protocol of the obtained runtime rule.