SimplytheBest Security Scripts
The simply the best collection of security scripts
The 5 best security scripts
The ultimate security plugin that will take your WordPress security to a whole new level. Features a security points grading system, enable groups of security features, apply firewall rules progressively and more.
Free Open Source LGPLv2.1
A standards compliant HTML filter library written in PHP. HTML Purifier will not only remove all malicious code (XSS) with a thoroughly audited, secure yet permissive whitelist, but it will also make sure your documents are standards compliant.