Shady scheme requiring computers to be set up (4)
I believe the answer is:
scam
'shady scheme' is the definition.
(I've seen this in another clue)
'computers to be set up' is the wordplay.
'computers' becomes 'Macs' (Apple Macs).
'to be set up' is a reversal indicator (in a down clue, letters go up).
'macs' backwards is 'SCAM'.
'requiring' acts as a link.
(Other definitions for scam that I've seen before include "Fraud, dishonest scheme" , "'A con, deception (4)'" , "Swindle, fraud (colloq.)" , "Fraudulent trick or swindle" , "Rip off" .)