Today we have released IntelliJ IDEA 2016.1.2. In addition to the usual functionality fixes, this update addresses two important security issues. The vulnerabilities, in various forms, are also present in older versions of the IDE; therefore, patches for those are also available. It is strongly recommended for all users to install the update as soon as possible.
Find more information about the vulnerabilities, the affected versions and ways to update in this special blog post: http://blog.jetbrains.com/blog/2016/05/security-update-for-intellij-based-ides.
UPDATE: If you’re running on OS X and the IDE doesn’t start after installing the update, please refer to https://intellij-support.jetbrains.com/hc/en-us/articles/208516145 for workarounds.