Criminal hears about new opening for someone to control and exploit (7)
I believe the answer is:
harness
'control and exploit' is the definition.
(I've seen this before)
'criminal hears about new opening for someone' is the wordplay.
'criminal' indicates an anagram.
'about' is an insertion indicator.
'new' becomes 'n'.
'opening for' indicates taking the first letters.
The first letter of 'someone' is 's'.
'hears' is an anagram of 'hares'.
'hares' enclosing 'n' is 'harnes'.
'harnes'+'s'='HARNESS'
'to' is the link.
(Other definitions for harness that I've seen before include "Straps and fittings for horse control" , "Control and exploit" , "Restraint" , "Supporting gear" , "Horse's gear" .)