Computers set up for fraud (4)
I believe the answer is:
scam
'for fraud' is the definition.
(scam is a kind of fraud)
'computers set up' is the wordplay.
'computers' becomes 'Macs' (Apple Macs).
'set up' says the letters should be written backwards (in a down clue, letters go up).
'macs' written backwards gives 'SCAM'.
(Other definitions for scam that I've seen before include "Con trick" , "Fraud, dishonest scheme" , "Fraudulent trick or swindle" , "Fraudulent scheme, swindle" , "Screw" .)