Wrong: https://en.wikipedia.org/wiki/Linux_malware#Threats
Free software can have vulnerabilities. There is nothing magical in the free software definition that makes it not have vulnerabilities. Technically speaking, free and proprietary software are the same: software. In fact a same piece of software can be at the same time free and nonfree, if it is simultaneously distributed under a free software license and under a nonfree software license.
The rather low popularity of GNU/Linux is the main reason why there are not many viruses/troyans/worms targeting it. Then, there is the fact that GNU/Linux users usually not run as root, so the vulnerability must allow privileges escalation to be actually dangerous. More generally, GNU/Linux users often are tech-savvy what makes it harder to trick them into installing malware (e.g., in attachment of an email). Finally, it looks like free software generally has less vulnerabilities (but that is not a direct consequence of the software being free). For example, Apache is the most popular Web server and, yet, viruses/trojans/worms do not target it.
About Wine (which can be used to run free software that only exists for Windows): are there users running it as root? If so, why?
