@phpdeveloper.org
While not directly PHP-related (it could happen to any web language), this new post from Chris Shiflett today displays a major, recent example of how Cross-Site Request Forgeries can be a huge problem for you and your site.
In the comments to my article on CSRF, someone questioned whether CSRF is really anything worth worrying about. Rather than give a hypothetical example, I can point to a real one that is getting some attention today:
This attack seems pretty harmless (I'd rather not discuss ethical concerns), but it demonstrates something very powerful - a combination of XSS and CSRF.
As if one of them wasn't bad enough, you especially need to watch for XSS attacks - they can be a precursor (and even help out) to a CSRF attack. Be sure to check out Chris' articles on CSRFs and foiling them for more information...
UPDATE: Ilia also has this post on his blog concerning the issues surrounding this worm as well.