Separated another script,in another folder using another DB? For security

For a website, sometime we used more than a script that
separated, yes separated and dont have connection at all each other
for example domain.com is a forum, using vbulletin domain.com/blog
is a blog, using wordpress domain.com/store is ecommerce, using
oscommerce domain.com/article is article cms, using joomla etc so
for security best practice, like if