This malware's the stuff of legends (6)
I believe the answer is:
trojan
'this malware's the stuff of legends' is the definition.
The definition suggests a singular noun which matches the answer.
This is the entire clue.
Can you help me to learn more?
(Other definitions for trojan that I've seen before include "Hard grafter (from an ancient city?)" , "This legendary horse was wooden and hollow" , "Traditional type of horse" , "Work like a . . . . . ., with great energy and endurance - ask Helen" , "This horse once concealed Greek warriors bent on breaking a siege" .)