Security breach (4)
I believe the answer is:
leak
'security breach' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for leak that I've seen before include "(Politically motivated) seepage?" , "Divulgation" , "Liquid loss sounds like a vegetable" , "Lose water" , "Accidental hole allowing liquid to escape" .)