On Jemjabella.co.uk, there's a quick post with a few helpful hints of spotting the insecurity inside of some scripts.

With the current surge in "hackings" (or rather: script kiddies exploiting known holes to deface websites that don't support their view on the war) I've been going through a lot of scripts to find common and easy to fix vulnerabilities. With my fingers crossed, and perhaps a naive hope that people don't release scripts with massive holes anymore, I've been sorely disappointed.

They list out a few different things to watch out for, including potential SQL injection points and the unchecked inclusion of files via include(). It's some pretty basic stuff, so don't expect much new from the post, but it's a good reminder of some of the simple things we all, as developers, need to watch out for.