I've never tried to hack sites. I've just followed security guidelines. Now I want to try to develop more safety.
Is there are any "training sites" with holes and "exercises", with SQL injections, redefining global variables, XSS and other kind of holes. Kind of hacker sandbox.
Google has just the thing, try Gruyere
This codelab is built around Gruyere /ɡruːˈjɛər/ - a small, cheesy web application that allows its users to publish snippets of text and store assorted files. "Unfortunately," Gruyere has multiple security bugs ranging from cross-site scripting and cross-site request forgery, to information disclosure, denial of service, and remote code execution. The goal of this codelab is to guide you through discovering some of these bugs and learning ways to fix them both in Gruyere and in general.