This patch provides protection against several types of security-related issues, including information leaks, request forgeries, and cross-site scripting. - Added Jul 7, 2015
Note: if you have previously applied patch PATCH_SUPEE-6285_CE_1.9.1.1_v1, please revert it and apply PATCH_SUPEE-6285_CE_1.9.1.1_v2.
More information on reverting and applying patches is available here.
Make sure to install SUPEE-5994 patch first.
Magento Community Edition version 1.9.2 already includes the latest version of the patch.
More information about the individual issues addressed by this patch is available in the patch release notes.
More details about this patch could be found here.