How can I use time-series transforms for detecting malware?
The point seems to be moot. An attacker could hide in noise. Any meaningful interpretation of the question appears to aim for temporal regularity of attacks. Maybe an attack is temporally regular, but so is users' behavior. So, there might be lots of applications for transforms in malware detection, but none of them appears to promise any insight on how to recognize or intercept it.

From a computer science standpoint i would say that ,,recognizing malware'' is akin to the problem of recognizing two functions as equal, which in general is a proof, which is not computable in any ordinary sense. It would probably amount to proving P=NP. Any ,,heuristic'' recognition of malware can be evaded that way. The only system capable of actually and reliably recognizing malware appears to be a conscious human being.