A method and a system for detecting one or more security vulnerabilities. The method comprises providing test instructions for an application, such as a web application or a client server application, adding test code to a code segment of the application according to the test instructions, sending at least one message to the application according to the test instructions at runtime thereof, monitoring test information pertaining to at least one reaction of the application to the at least one message during an execution of the test code, performing an analysis of the at least one reaction, and detecting a presence or an absence of at least one security vulnerability according to the analysis.