1. A computer-implemented method for testing an application for cross-site scripting vulnerabilities, comprising the steps of: under control of at least one processor, (a) for at least one field, parameter or URL of the application, submitting a request in which the field, parameter or URL contains a test slug consisting of an encoded or non-encoded test character or a string of test characters between two default slugs; (b) determining if the application returns the test slug with the test character or string of test characters and whether any of the test characters in the test slug are transformed or not transformed in the returned test slug; (c) storing in tangible computer memory the result of the determinations made in step (b); and (d) repeating steps (a)-(c) for a plurality of different test characters or strings of test characters.