Linux is (very, very closely) based on UNIX. As an old Bell Labs guy I
love it!
I run Windows (reluctantly) on my desktop since there is
one program I use that does not have a good Linux alternative -- Diamond Cut software for restoring and editing audio files.
My netbook runs Ubuntu, a Linux "distro" (distribution -- the underlying Linux is nearly identical among most major distros -- the user interface, desktop, etc. vary).
I don't have experience with Windows 7 or 8, but the Windows systems I'm familiar with will happily run anything that ends in .exe, .bat, or any one of many other file extensions without ever even mentioning it to the user. This is a little like a kid who happily runs up to every stranger he meets and asks for candy.
Linux doesn't need file extensions, and generally needs
you to tell it to run something before it will run it. Even then, it won't even allow
you to run something that will make system-wide changes without prompting you for the system password. That's the first hurdle a malware writer has to jump.
Next, different operating systems will use the same hardware very differently. A virus written for a computer running Windows cannot affect that same computer running Linux. So, malware writers would have to write twice as many viruses to cover the field. It's generally not worth it -- too many people and businesses are happy to run the computer they bought and never mess with the OS. (The big exception to this is for network servers, which make great distribution systems and where a significant percentage run Linux based Apache software. It's still pretty tough to do, though.)
When my daughter started using her computer for homework assignments, back when she was in 5th grade, I wiped Windows from an old desktop and installed Ubuntu. Sure enough, one of the sites she was
directed to for a homework assignment ran an infected banner ad. She flew into a panic. The ad used Javascript to hijack her browser (Javascript on Linux runs anything that Javascript on Windows runs), and popped up a fake alert that she had malware installed and a fake virus scan. However, the real malware payload
DID NOT INSTALL. She got panicky and asked me to help. I pointed out that Linux does not call it's hard drive C:, that she didn't have any of the Windows specific directories, dlls, etc. Closing the browser solved the problem. It worked fine when she opened the browser again.
To test-drive Linux get a
Live CD or download. It will run the Operating System from RAM and it
will not mount your hard drive, so you cannot affect anything there -- unless you choose to install. There are tons of very professional home and office software available, most free, including office suites, music and videos, Skype, etc.
I've attached screenshots of my daughter's fake attack. Her computer had no infection but some of her classmates, running Windows, got nailed.