What are the techniques for exploiting computers today?

Question

I've just read "Hacking: The Art of Exploitation" and I'm interested in this subject. The thing is, this book seems irrelevant to hacking now that OSes have non-executable stacks, canary values on the stack, etc.

So, how what methods are used now to exploit computers?

Edit: Sorry, I wasn't clear. I was wondering about how hackers attack computer programs, not websites

Answer 1

Off the top of my head (and the inspiration behind my user name) are SQL injection attacks.

I have inherited a number of sites I have had to clean up due to ad-hoc queries not properly scrubbing their data.

Answer 2

When it comes to Web attacks, the OWASP Top 10 for 2010 (here's the PDF) will tell you which attacks you ought to protect yourself against.