Different security group obscure leak about island (7)
I believe the answer is:
unalike
'different' is the definition.
(not like something else)
'security group obscure leak about island' is the wordplay.
'security group' becomes 'un' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'obscure' is an anagram indicator.
'about' is an insertion indicator.
'island' becomes 'i' (geographical abbreviation).
'leak' anagrammed gives 'alke'.
'alke' going around 'i' is 'alike'.
'un'+'alike'='UNALIKE'
Can you help me to learn more?
(Other definitions for unalike that I've seen before include "Dissimilar" , "poor match" , "different" , "Differing from each other" , "Not similar to one another" .)