On first running, Trojan:W32/Murofet.A checks if the system already has a specific key value set:
- HKCU\Software\Microsoft Microsoft=1
This key value acts as an infection marker and is set by another program (presumably an accomplice to this malware). If this infection marker is found, Murofet.A will not proceed any further.
If the infection market is not present, this malware will spawn a thread that downloads an arbitrary file from the Internet.
To download the file, the malware connects to a domain whose URL is randomly generated based on the current system date and time. The pattern of the generated URL is:
where the [generated_domain] is a series of lowercase ascii characters from a to z and [generated_tld] will be one of the following: "biz", "info", "org", "net", or "com".
If there is at least one successful download, the malware will save the downloaded file to the %TEMP% directory, then verify the file's integrity against an embedded public key that is generated by the author using the SHA hashing algorithm. If verification is successful, the downloaded file is executed.
If the download or verification is not successful, the malware will move on to generate another download URL; it attempts to repeat the process up to a maximum of 800 times or until it is successful.
At the time of testing, there were no successful file downloads.