A system and method for finding vulnerabilities and tracing an end result associated with a vulnerability to its origins in user data. A user data source containing an ordered sequence of user data items may be a data file. In one embodiment the method for identifying, in the user data source, the origins of the end result, includes associating with each user data item a location identifier identifying the location of the user data item in the sequence of user data items executing instructions with a virtual machine, associating with each result the location identifier of the data item when one argument is a user data item and a tag when more than one argument is a user data item. This process may be continued until the end result is obtained. Subsequently, the method may include stepping through instructions with the virtual machine in reverse order, to tracing the origins of the end result to each of the user data items contributing to the result.