Historically, I think the answer is just that the NSA doesn't even try.
There are some three-letter agencies that do work on fighting malware, often by partnering with relevant companies like Microsoft (who was a major anti-malware player here too). I know the FBI does so publicly, and some government groups invite large companies to low-secrecy briefings on security.
But I've never heard a mention of the NSA 'fighting' malware that isn't obviously governmental. Even if they knew about the exploit, used the exploit instead of disclosing it, and are well-placed to fight it, I think that's just filed under 'not my department'.
There are some three-letter agencies that do work on fighting malware, often by partnering with relevant companies like Microsoft (who was a major anti-malware player here too). I know the FBI does so publicly, and some government groups invite large companies to low-secrecy briefings on security.
But I've never heard a mention of the NSA 'fighting' malware that isn't obviously governmental. Even if they knew about the exploit, used the exploit instead of disclosing it, and are well-placed to fight it, I think that's just filed under 'not my department'.