Today, WordPress 4.2.4 was released as an important security fix. This update comes just one week after the release of WordPress 4.2.3.
4.2.3 caused quite a few issues with many sites as it changed the way WordPress uses shortcodes. This caused many sites to break their formatting when they relied of shortcodes to display content. The release team did not give a lot of warning to this change, although it was important to close the security hole with cross-site scripting.
This update, 4.2.4 supposedly fixed the issue sites were having with 4.2.3, so many plugin and theme authors will be happy. This update also addresses more issues with cross-site scripting as well as a SQL injection vulnerability.
You should update your site right away and always remember to backup your site before updating!