Criminal gang with modern technology (6)
I believe the answer is:
bandit
'criminal' is the definition.
(type of thief)
'gang with modern technology' is the wordplay.
'gang' becomes 'band' (I've seen this before).
'with' means one lot of letters go next to another.
'modern technology' becomes 'it' (Information Technology).
'band'+'it'='BANDIT'
(Other definitions for bandit that I've seen before include "Armed brigand" , "Outlawed robber" , "Violent outlaw" , "Thief" , "Armed outlaw" .)