I think buwaya was trying to make the point that since home users of Linux download many free apps from just about anywhere, whose to say this type of virus isn’t hidden in anything else?
Many ISPs who provide service to home users block the outgoing SMTP port, just for this reason. So if a home user did have such malware, it wouldn’t be very useful.
I gather from your comments that you are not that familiar with the ‘nix OS. Linux does not have many “apps” in the same way that the ‘doze system does. There are, however, many programs available for different functions available from known and trusted sources called “Repositories” or “repos” for short.
If I need an app for a particular useage I go to the repos to download what I need, either from the Stable / Main for the most reliable version, or to the Unstable / Testing pool for newer versions. For more cutting-edge versions or newer and still-developing programs I can always look in to what SourceForge has available, or even Freecode (formerly Freshmeat) for the latest or just-beginning (alpha and beta -level) projects if I am really curious.
People running network servers do not do even that, since the server exists for one function only and that is most definitely NOT installing non-relevant programs. Since anyone who has a website hosted may have their server running on BSD, Linux, or Unix, this potentially affects any user running any machine on the net. A server compromise to effect spamming is not a small problem.