Enthuse everyone around with security system (8)
I believe the answer is:
firewall
'security system' is the definition.
(I know that firewall is a type of security system)
'enthuse everyone around with' is the wordplay.
'enthuse' becomes 'fire' (fire someone up).
'everyone' becomes 'all' (all people).
'around' is an insertion indicator.
'with' becomes 'w' (short for with).
'fire'+'all'='fireall'
'fireall' placed around 'w' is 'FIREWALL'.
(Other definitions for firewall that I've seen before include "network protection" , "Computer security system against online attack" , "Software protection for computer" , "A protective system" .)