Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
If you use Linux instead of Microsoft Windows, its free availability may well be a deciding factor. But the fact that virus and malware contamination are less likely to take down your Linux computers are no doubt essential influencing factors as well.
But does using a more popular Linux distro like Cononical's Ubuntu make your system more or less vulnerable than a Linux-on-a-stick variety such as Puppy Linux? More likely than not, if you use any Linux distro, you will compute in a relatively strong security envelope.
Still, some aspects of the open source community are pushing out hybrid Linux distributions that claim to be more secure than your otherwise plain-vanilla Linux distro of choice. So if you want a more hardened Linux configuration, you have options.