A lot of suggestions would tell you how to write secure sites, but if you really want the guts, learn how to break the site. Go to the library and pick up some

A lot of suggestions would tell you how to write secure sites, but if you really want the guts, learn how to break the site. Go to the library and pick up some network security books, and focus on the website security sections (sql injections, exploiting the parameters sent to a website, trying to learn the sites using their error messages to ssl to domain spoofing). For one, this is actually a lot of fun, but more importantly, now you'll always be thinking how to exploit the code you write, and doing so will allow you to realize mistakes very quickly.