On the O'Reilly OnLamp.com site, there's a bit more in-depth look at using the (now infamous) Google Code Search to locate issues with scripts that have been collected over time.

I've written about using Google to find security flaws in the past. However, thanks to Google Code Search, it is now easier to scan publicly available source code for potential security issues. The idea is query Google Code Search using techniques previously reserved for local static code analysis.

The examples he gives include a search for SQL injection in a Java application, a SQL injection in a PHP application, and a cross-site scripting problem in a PHP app blindly echoing out the user's input.

He also includes a few links to some code analysis tools that can be used to help prevent some of these issues - Flawfinder, RATS, and SWAAT