User gaining unauthorised access to IT systems (6)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
hacker
(Other definitions for hacker that I've seen before include "Novice golfer" , "Person who breaks into computer systems" , "Modern burglar who breaks in to computer systems" , "Modern criminal who breaks into computer systems" , "Jim -- (Yes, Minister)" .)