What is alfUIplugin.plugin? I'm cleaning old 3rd-party stuff out of my /System/* subdirectories on 10.11. And I noticed in /System/Library/UserEventPlugins/ the following file: alfUIplugin.plugin. The file size is zero bytes! And the date modified is in 2012, three years ago; surely it's not part of El Capitan. Right?

I can safely delete this...right?
From Apple Support :    


  I was chasing this down myself. It looks like this
  plugin is used for ALF - Application Level Firewall. ... like the
  System Preferences/security setting/firewall possibly.


_


  I too am seeing those errors after updating to Mavericks on my MacBook
  Pro.  And, I cannot find any info on what alfUIplugin.plugin is
  either.  However, upon going to /System/Library/UserEventPlugins
  folder, I noticed that the plugin file is 0KB.  On my Mac Pro, which
  is still running Mountain Lion, it is 20KB and on Snow Leopard it's
  like 50KB.


https://discussions.apple.com/thread/5505336