How your secure your Linux system
Are you running Linux just because you think it's safer than Windows? Think again. Sure, security is a built-in (and not a bolt-on) feature and extends right from the Linux kernel to the desktop, but it still leaves enough room to let someone muck about with your /home folder.
Linux might be impervious to viruses and worms written for Windows, but that's just a small subset of the larger issue. Attackers have various tricks up their sleeves to get to those precious bits and bytes that make up everything from your mugshot to your credit card details.
Computers that connect to the internet are the ones most exposed to attackers, although computers that never get to see online action are just as vulnerable. Think of that ageing laptop or that old hard disk you just chucked away without a second thought. Bad move.