... stop criminals acquiring more openings for fraud (4)
I believe the answer is:
scam
'for fraud' is the definition.
(scam is a kind of fraud)
'stop criminals acquiring more openings' is the wordplay.
'openings' suggests taking the first letters (I've seen 'opening of' mean this).
The initial letters of 'stop criminals acquiring more' is 'SCAM'.
(Other definitions for scam that I've seen before include "'A con, deception (4)'" , "fiddle" , "Confidence trick, swindle" , "Screw" , "rook" .)