MS Silverlight. If still not signed, you might have to run it from the System Preferences => Security and Privacy => "Click the lock to make changes." => Allow apps downloaded from: Anywhere.
No need to revert to: Allow apps downloaded from: Mac App Store and identified developers. Just keep it as "Anywhere". (June 6, 2015.)
And possibly other software
Adobe Acrobat, full version. (N.B. Almost no reason to have the read-only Acrobat installed (much less updated) since Mac OS comes with competent PDF reader, Preview.)
If Java installed, use Java Control Panel, available through the Java control panel in System Preferences (opens in a separate window).