I recently upgraded from FAQ Book 3.0.x to 3.3.7. Now some pages somewhere on the internet still link to the old categories. If someone views such a page, then an error message is displayed which reveals potentially dangerous data such as:
1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 26 SQL=SELECT content.id AS iid, content.title AS title, content.alias AS alias, content.introtext AS introtext, content.fulltext AS text, content.catid AS parent, content.created_by AS author, content.created AS date, content.publish_up AS date_publish, content.hits AS hits, content.images AS images, content.featured AS frontpage FROM #__faqbookpro_content AS content WHERE content.state = 1 AND content.access IN (1,1,5) AND ( content.publish_up = '0000-00-00 00:00:00' OR content.publish_up <= '2016-11-28 12:02:33' ) AND ( content.publish_down = '0000-00-00 00:00:00' OR content.publish_down >= '2016-11-28 12:02:33' ) AND content.catid = 11 AND content.language in ('en-GB','*') ORDER BY content.
See for example:
https://www.enigmail.net/index.php/en/faq?view=category&id=11
