Well if you recently upgraded/updated your WordPress website to 4.2.3 and it didn’t break your website you need not worry. But if it did break your website here are some of the possible reasons why it might have caused it in the first place:
WordPress.org core team has actually made changes to the shortcode API as has been listed here: https://make.wordpress.org/core/2015/07/23/changes-to-the-shortcode-api/
What happened due to this was that several plugin developers had used Shortcodes API in the way it suited their requirements and their plugin.
Now with changes to Shortcode API their whole plugin/code came crumbling down and basically breaking the websites which used these plugins.
Most common plugins which got affected were:
Since then users community have been posting remarks about WordPress auto background updates and whether or not its a good idea.
WordPress.org core team now needs to understand that website development agencies, plugin developers and theme developers all form part of their group and they should have announcements prior to releasing of any major update/changes like this which might possibly break a theme or plugin.