How do i find a vulnerability , i have watched many tutorials regarding the tools used in hacking but none seem 2 be effective on secure applications So what i am looking for is 0day vulnerabilities . How do i find them , how to detect that a particular application is vulnerable to an exploit or is showing some tendency for it. I know Nessus and Nikto are there for these purpose but said earlier they r not worthy when it comes to some super secure applications. So how is it that vulnerabilities are detected how do i start to find them because whichever application i pickup it seems so vast to explore , it is so impossible to find a vulnerability. PLZ HELP Which is the quickest way to start ?