In computing, an underhand beast (5)
I believe the answer is:
mouse
'beast' is the definition.
(mouse is a kind of beast)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for mouse that I've seen before include "computer operator" , "shy and timid type" , "Timid creature" , "Small rodent and cursor controller" , "Cursor control" .)