It's a definite possibility. However, with Android and iOS many people are learning that the world doesn't end after Windows and Ubuntu is very user friendly.
The typical PC user uses a web browser, an office suite and videogames. With Chrome you have an excellent web browser regardless of OS; LibreOffice is fine for many users and it's interface is similar to that of Office pre-Ribbon, which many appreciate. Games have been a painful issue, but with browser-based games and Valve porting to Linux it's getting really better.
I believe it's a matter of time until users begin questioning the Microsoft tax when they can get a useful OS sans viruses and malware for free.
No doubt there will be more attempts, but there are reasons to expect they won't be as successful. The default method of installing applications on Windows and Mac is to download an executable from the internet and run it as Administrator. The default method of installing applications on Linux is to get them from the package manager, and binaries downloaded from the internet don't have the execute bit set by default.
I don't mean to say that Linux is totally immune from malicious software, but it's a much harder target. You're in the position of having to either get malicious software into the repositories, convince users to do something arcane and atypical with binaries downloaded from the internet, or exploit security vulnerabilities in installed software on an OS with a package manager that auto-updates everything to the latest patch on a regular basis. None of those is anywhere near as easy as "click here to see Anna Kournikova naked" or exploiting known Java vulnerabilities that Apple was kind enough to leave unpatched for like a year.
