Employer’s new ruse (4)
I believe the answer is:
user
'employer's' is the definition.
(someone who employs or uses something)
'new ruse' is the wordplay.
'new' indicates an anagram.
'ruse' with letters rearranged gives 'USER'.
(Other definitions for user that I've seen before include "One taking drugs" , "Consumer" , "junkie" , "Person who takes drugs" , "With 1a [NEW] he'll need different login" .)