Greek letter judged to be illegally copied (7)
I believe the answer is:
pirated
'be illegally copied' is the definition.
(I've seen this in another clue)
'greek letter judged' is the wordplay.
'greek letter' becomes 'pi' (letter from the Greek alphabet).
'judged' becomes 'rated' (rating is a kind of judging).
'pi'+'rated'='PIRATED'
'to' is the link.
(Other definitions for pirated that I've seen before include "Copied" , "knocked off" , "Published without permission" , "Used in defiance of copyright" .)