All updates to Microsoft Silverlight include functional, performance, reliability and security improvements and are backward compatible with web applications built using previous versions of Silverlight.

• Fixes Security issue described in the following Microsoft Knowledge Base article: 2636927 MS12-034: Description of the security update for Microsoft Silverlight: May 8, 2012
• Fixes an issue where “Best Effort” Silverlight Digital Rights Management Output Protection levels failed on some machines.
• Fixed a failure to update OOB applications that are configured to use elevated trust when in browser.
• Fixes an issue where persistent license acquisition would fail when a customer upgrades from Silverlight 4 to Silverlight 5.
• Fixes an issue where certain character combinations can cause Silverlight application to crash.
• Fixes an Access Violation described in the following Connect issue https://connect.microsoft.com/VisualStudio/feedback/details/719572
• Fixes an issue where the SL5 plugin displays blank window after installing a font with a font name that starts with “&”.
• Fixes an issue where moving a focus to TextBox or RichTextBox after moving a focus to ItemsControl causes IME to be disabled.
• Fixes an issue where Silverlight would not play content which required Output Protection.
• Fixes a Silverlight DRM issue where some customers encounter hardware ID mismatch errors which can only be resolved by re-individualization.
• Minor version number incremented to 1 (5.1.10411.0) and the build number (5.1.10411.0) count was restarted at 1 (104011) because the build numbers in 2012 and subsequent years would have exceeded the 16 bit (unsigned) integer limit for build numbering in versions.  Incrementing the minor version number to 1 and restarting build numbering at 10000 would maintain the ability of subsequent Silverlight versions to update previous versions.