Sleepwalker: Passive Backdoor with Its Own Command Language

in my script kid days, ( 30 years ago ) I did something similar for linux , using raw sockets and I think with ETH_P_ALL. embedding into a an already existing regular linux process ( recompiling the source code ) the problem was high cpu usage of the process when network usage was intensive. of course it did't survive when the OS updated the program.

This is very cool. Definitely seems like either an early or one-time, targeted attack by someone with good know-how and significant resources, even if it itself is not top-tier. Pretty cool find!

What would be considered “top-notch” or “top-tier”? Something never found?