This is a Windows system installed file with Windows File Protection (WFP) enabled.
There are 42 versions of ntshrui.dll in the wild, the latest version being 6.3.9600.16384 (winblue_rtm.130821-1623). It adds a context menu to the Window's shell named Sharing. The average file size is about 385.04 KB.
(Note, the behaviors below are for all versions of ntshrui.dll, select a unique version for details.)
Located in the registry at 'SOFTWARE\Microsoft\Windows\CurrentVersion\Shell Extensions\Approved'
United States installs about 51.89% of Shell extensions for sharing.