Hiding when they're carrying out a security check (9)
I believe the answer is:
screening
'hiding' is the definition.
(I know that screening is a type of hiding)
'they're carrying out a security check' is the wordplay.
I cannot really see how this works, but
'check' could be 'screen' (synonyms) and 'screen' is present in the answer.
This explanation may well be incorrect...
'when' acts as a link.
Can you help me to learn more?
(Other definitions for screening that I've seen before include "broadcast" , "Showing (of a film)" .)