A common and frequent mistake made by many webmasters is not to keep their scripts up-to-date. What are scripts? Scripts are web-based applications (apps) – typically written in PHP and CGI-Perl, but also Python, ASP, Ruby on Rails, etc. This can be a critical mistake.
You could expose your web server, website, and users to security vulnerabilities. Vulnerabilities are commonly discovered in apps. Sometimes they arise from changes in the app code from a previous update, or were missed and only just discovered due to recent exploits by hackers who discovered the vulnerability. Sometimes they arise from changes/updates in the underlying framework: web server, programming language like PHP. Either way, it is important to keep your apps updated as your best defense from having your site and users exploited. This is particularly important in regard to forum, blog (especially WordPress), and CMS (content management system) apps as they are often exploited. Note that it is common that the vulnerabilities can be exploited to exploit other unrelated apps or gain access to web server files (like password files) and processes. Stay ahead of the hackers.
So, stay on top of matters, and on a regular basis, check your app version numbers with the current version number through the app author. If your version is out-of-date, update your app. Keeping your apps up-to-date also ensures your apps have all the new available functionality and features. A win-win situation.
My two cents worth.