Sorry if this is sarcasm, not quite got it. But Linux is no more malware free than any other operating system. What I have heard before is Linux is "virus free" which is something different. Any operating system can get malware simply because the weakest link is the meat bag behind the keyboard who can click a dubious link for free malware installation.
Linux/Unix does make installing malware accidentally much harder but it is not impossible. Completely malware immune systems is a fantasy in terms of full far operating systems.