Depending on its variant, malware is largely obtrusive - in the sense that it leaves quite an extensive papertrail of evidence …
The general process of a malware attack can be broken down into a few broad steps, which will generate data:
Delivery: his could be of many methods, for example, USB (Stuxnet) or PDF attachments through “Phishing” campaigns.
Execution: What does it do? If it encrypts files and leaves a ransom note, it is Ransomware. If it records keystrokes it is a Keylogger. If it collects personal preferences to display adware, it is Spyware. This stage can only be understood through analysing the sample.
Maintaining persistence (not always the case!)
Propagation (not always!)
There are two categories of fingerprints that malware may leave behind on a Host after an attack:
Host-Based Signaturesare the results of execution and any persistence performed by a Malware. For example, has a file been encrypted? Has any additional software been installed? These are two of many host-based signatures that are useful to know to prevent and check against further infection.
Network-Based Signaturesare the observations of any networking communication taking place during delivery, execution and propagation. For example, in Ransomware, the Malware contacted which wallet for Bitcoin payments? Or for example, a large amount of “Samba” Protocol communication attempts may be an indication of WannaCry infection because of its use of “Eternalblue”.