Justify copper's infiltration of Windows file (6)
I believe the answer is:
excuse
'justify' is the definition.
(I know that excuse is a kind of justify)
'copper's infiltration of windows file' is the wordplay.
I cannot quite understand how this works, but
'copper's' could be 'cus' (chemical symbol) and 'cus' is present in the answer.
The remaining letters 'exe' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for excuse that I've seen before include "Absolve" , "Let off or make allowances for" , "Mitigate; forgive" , "Allow to be released from a duty" , "Defence of offensive behaviour" .)