... claiming their favorite operating system is free from such threats ...

No, they claim that Linux is far less vulnerable structurally, and historically far freer of exploits. To the point that a single exception rates as "news".

... it gives a hacker absolute control over the server.

No, it "allows a person to execute ANY command with the privileges of the user running the ircd". Do you run ircd as root?

A similarly infected Windows file in the wild would be detected within days if not hours after a routine virus scan ...

And then either Microsoft or the vendor might choose to release a patch, or they might not, and there's no reason to expect that the exploit wouldn't have already closed the door behind itself on the millions of machines now zombied.

Linux users who believe they can't be infected by malware are simply wrong.

They're also rare.