Hire third party to expose informer (9)
I believe the answer is:
outsource
'hire third party' is the definition.
I know nothing about this answer so I cannot tell whether this works.
'expose informer' is the wordplay.
'expose' becomes 'out' (to out someone is to expose them).
'informer' becomes 'source' (I am not sure about this - if you are sure you should believe this answer much more).
'out'+'source'='OUTSOURCE'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for outsource that I've seen before include "Use contractors" , "Subcontract work" , "Contract (work) to an external supplier" , "Avoid working oneself" , "Use external supplier" .)