Security Wall improves the global concrete5 security. By boxing c5 inside a powerful security framework, Security Wall can block most of web-based attack. This is absolutely a great feature when a new c5 version come out and some changelogs are released to public. Until you upgrade the c5 core it's very easy for people to attack your site (this happens for every CMS, not only c5). Security Wall is actually based on PHPIDS, a simple to use, well structured, fast and state-of-the-art security layer for your PHP based web application.
Security Wall is now disabled by default!
Security Wall can cause a lot of problems while editing your site. If you find any strange behaviour maybe it's because of it. I'm actually working on a new version when blacklisting is more flexible. Anyway it's advised to activate user bypass for trusted users/groups and to check log page regularly if something is going wrong.
Security Wall actual intended use is for sites that doesn't need user interaction.