If you're interested in security, you've probably already heard of security-focused Linux distros such as Tails, Kali and Qubes. They're really useful for browsing anonymously, penetration testing and tightening down your system so it's secure from would-be hackers. Here are the strengths and weaknesses of all three.

If you're troubleshooting your PC or installing a new operating system, you'll occasionally have to "boot it from a disc" or USB flash drive. Here's what that means and how to do it.

Windows: Whether you're looking to try out Linux or create a Windows troubleshooting tool, LiLi will create a powerful Linux thumb drive, letting you pick your distribution, save data between reboots, or even launch your mobile OS right from Windows.

PCWorld provides a nice reminder of four good reasons everyone should have at least one live-booting, Linux-powered CD around: saving a system, security-conscious banking, repurposing old hardware with minimal OSes, and, well, simply testing out Linux.

If you want to boot into a live Linux environment but don't have a blank CD or thumb drive handy, you can actually boot right from your hard drive using GRUB and previously mentioned Unetbootin.

Windows: If you're tired of managing five or six different live CDs for testing and troubleshooting, free program XBoot will help you merge them all onto one DVD or thumb drive, complete with a handy menu to choose between them.

Have you ever wanted a nice personalised copy of Ubuntu to take around with you? Even if you aren't well versed in the terminal, Remastersys makes it very easy to create a customised live CD from the Ubuntu you already have installed.

We love a good live CD, but what if your favourite one doesn't quite have every application or tweak you need? Here's how to roll your own Ubuntu Live CD, with all the packages you want and some nice customisations to boot.

Windows: Can't decide whether you should commit your spare thumb drive to Windows recovery, Ubuntu or some other live-booting OS? Run MultiBootISOs on your USB drive, and you won't have to choose — you'll just choose between them at start-up.

Add Registry repair and editing to the list of Windows repairs you can make with a live Linux system, even if you can't boot into Windows. An Ubuntu Forums member shows how to make specific registry tweaks and fixes from inside Ubuntu.

Live CD: If you've been meaning to make a comprehensive backup of your system but available tools seemed a bit too arcane and command-line dependent, Redo Backup is a Linux Live CD with a simple user interface and easy to use tools.

If your PC has been experiencing strange system crashes, or even the dreaded blue screen of death, it's worth running some tests to check your system hardware. Luckily the Ubuntu Live CD has some tools built right in.

Plenty of utilities can recover deleted files, but what if you can't boot your computer, or the whole drive has been formatted? Here's how to dig deep and recover the most elusive deleted files, or even whole partitions.

We've highlighted options for properly erasing your hard drives in the past (some simple, some involving hammers); in a similar vein, our friends at How-To Geek dive into the specifics of securely wiping your hard drive with an Ubuntu Live CD.

All systems: Fedora 13, the latest version of the Linux desktop code-named Goddard, is available for testing out on a live CD, a USB stick, or, for the brave, hard drive installation. Automatic printer drivers, better graphics support, and more is included.

When Windows goes wrong, it can go really wrong. Worse: Often it's extremely difficult to save your system from Windows itself. Here's how to use a simple USB drive to free space, remove viruses, rescue passwords and more from crunked Windows setups.

All platforms: Fedora's released a bootable beta of their upcoming 12th release, "Constantine", that speeds up system updates, makes Bluetooth an on-demand service, and optimises CPU and graphics performance on netbooks, among other improvements.

Windows: Want to try out a flavour of Linux or other LiveCD-based tool without installation or even having to exit Windows? MobaLiveCD has updated to include support for both LiveCDs and bootable USB devices.

Windows only: Free application uSbuntu Live Creator installs a Live CD from an ISO image onto your USB flash drive—much more useful, portable and easy to deal with than carrying around a CD.