Review top secret revenue's source after hacking (10)
I believe the answer is:
retrospect
'review' is the definition.
('retrospect' can be a synonym of 'review')
'top secret revenue's source after hacking' is the wordplay.
'source' says to take the initial letters (I've seen 'sources' mean this).
'after' means one lot of letters go next to another.
'hacking' indicates an anagram.
The first letter of 'revenues' is 'r'.
'top'+'secret'+'r'='topsecretr'
'topsecretr' anagrammed gives 'RETROSPECT'.
(Other definitions for retrospect that I've seen before include "A backward view" , "Hindsight" , "Contemplation of the past" , "Look at history" , "Survey of past events" .)