This is a Windows system installed file with Windows File Protection (WFP) enabled.
sens.dll has 45 known versions, the most recent one is 6.3.9600.16384 (winblue_rtm.130821-1623). The average file size is about 44.61 KB. This is a .NET Common Language Runtime (CLR) assembly.
(Note, the behaviors below are for all versions of sens.dll, select a unique version for details.)
Based on 40+ industry antivirus scanners, 5 of them detected the following malware.
United States installs about 33.33% of System Event Notification Service (SENS).