1. A system for detecting security vulnerabilities in web applications, the system comprising: at least one hardware processor, wherein the at least one hardware processor includes a block-box tester, and a client-side evaluator, the black-box tester is configured to interact with a web application at a computer server during its execution at the computer server, and identify client-side instructions provided by the web application responsive to an interaction with the web application, the client-side instructions are configured to be implemented by a client computer that receives the client-side instructions from the computer server; and the client-side evaluator is configured to evaluate the client-side instructions identified by the black-box tester, and identify a security vulnerability associated with the client-side instructions.