An improved information tracking procedure is provided. A precise information tracking procedure is performed for a sensitive value when an application is predicted to modify the sensitive value prior to the sensitive value reaching a data sink. The sensitive value comprises an attribute that may be linked to external knowledge to reveal sensitive information about an individual. In response to the application not being predicted to modify the sensitive value prior to the sensitive value reaching the data sink, a value-based information tracking procedure is performed. The value-based information tracking procedure comprises storing one or more values that are observed at a data source, and then determining whether or not each of these one or more values are observed at the data sink.