Internet is a plethora of information. Today millions of people are using website to access such valuable information. Due to cyber-crime website owner should learn to protect their assets from attacker. If the attacker manages to hack the website and its users account then that could be a threat. In order to prevent cyber- attack, website can be integrated with security mechanism such as Completely Automated Turing Test to tell computers and humans apart. But unfortunately it has been proven weak and attackers have managed to bypass the system. By using Machine Learning attacker can create a bot that can mimic human and break the system. This paper presents a replacement for such weak system. A system that is capable of preventing Denial of Service attack was proposed. Dynamic Word Cloud is integrated in place of text-based CAPTCHA successfully to increase the security level of the website and has proven to be a robust solution. Also solutions are provided to perform security testing on it so that one can prevent from future automated bot attacks.