If your PC is infected with malware such as a virus, or won’t boot because Windows files are corrupt, what can you do? We explain how to create rescue discs which can help.

Security software is essential for any PC which is connected to a network or the internet because of malicious programs like viruses, Trojans, spyware and other types of malware. No security software offers a cast iron guarantee, so there is always a small risk that your PC could become infected.

Malware can cause a variety of problems and it sometimes prevents Windows from starting. It can be difficult to remove and this is partly because when malware is running in memory, it can foil any attempts to remove it, restoring deleted files and settings.

There are other reasons your PC  or laptop could refuse to start up, ranging from a new piece of hardware to a newly installed application or corrupted system files.

One possible solution, so long as the problem is software-based, is a rescue CD. This is a special disc that can be used to start your computer.

The advantage of a rescue CD over normal virus and spyware removal tools is that it does not need Windows. The rescue CD has its own operating system, which is usually based on Linux, and because it does not need to start Windows, you are not trying to remove malware while it is running. This makes it easier to clean up infections.

What rescue discs do

Rescue CDs are mainly used to clean up malware infections that are difficult or impossible to remove in the normal way by running scanners and clean-up utilities in Windows. However, some offer a bit more and there may be file manager and file recovery utilities too. These would enable you to access the contents of the hard drive on a PC that will not start.

A file manager could be used to transfer documents, music, videos and photos to another drive, such as a USB disk. It may also be possible to recover lost and deleted files too.

What rescue discs don’t do

There are certain faults that rescue CDs cannot fix. They will not repair damaged Windows files that prevent a PC from working. However, some have a web browser and so they could be used to download missing or damaged files from the web. If you suspect that system files have been corrupted, the best solution is to boot from your Windows CD or DVD and use the repair option when prompted.

If you don't have a disc, see Microsoft's instructions for more information on creating a system repair disc.

When to use a rescue disc

A rescue disc should be used when you have tried and failed using the usual PC clean-up tools like antivirus and antispyware software, or you can’t boot the PC. Malware can embed itself deep within Windows and can disable security software. It can change file associations preventing you from running clean-up tools and block websites that provide software for removing malware infections. Booting from a rescue CD gets around all these problems because it doesn’t need Windows in order to work.

How to make a rescue disc

Don't wait until your computer has a problem: burn a rescue disc right now. Rescue CDs are usually provided as .iso files and after downloading one it must be burned to a CD. In Windows 7 or 8, right-clicking an .iso file displays a menu with an option to burn it to disc. Select it, insert a CD-R, cancel any auto-starting action, then click Burn.

Old PCs with old versions of Windows such as XP and Vista may need a utility like CDBurnerXP from cdburnerxp.se which does the same job. Some rescue systems can be written to a USB flash memory drive, which is then turned into a bootable device. This is useful for laptops that don’t have a CD or DVD drive.

In order to boot from your rescue disc, you may need to alter the boot order in the Bios. PCs are often set to start from a CD or DVD disc by default, trying the hard drive second. Rarely will they boot from a USB drive by default.

If your PC ignores your rescue disc or USB device, reboot and press F1, F2, F12, Del or whichever key launches the Bios setup utility. Look for the boot device or boot order among the settings and select the CD/DVD-Rom drive (or USB device) first and the hard drive second.

Rescue CDs download the latest virus definitions and updates and so an internet connection is required. There is usually support for Wi-Fi connections, but it won’t work on every PC or laptop. If in doubt, use an Ethernet cable to connect the computer’s network socket to your router, even if it means temporarily moving the PC closer to it.

How to create a Comodo Rescue Disk

Comodo’s disc is a 50MB download and it boots up into a version of Linux. Comodo Cleaning Essentials automatically starts and if there is an internet connection it automatically updates the virus definitions. If Wi-Fi doesn’t work, download the definitions database from here on another PC and copy it to a USB flash drive before starting.

Loading it isn’t obvious for non-Linux users and you must go to Tools, Import Signature Database, then go to Computer/mnt to see the drives attached to the PC. After updating the definitions you can click Smart Scan, Full Scan or create a custom scan. PCMan File Manager enables the PC’s disk to be accessed (go to /mnt to see the drives), and your files can be copied to another drive if the Windows disk has failed completely. There is also a web browser, which is useful for looking up information on the internet.

1. Download the rescue disc .iso file, then right click it and select burn disc image

Comodo Rescue Disc

2. Click Tools, Check for updates and the latest virus definitions are downloaded

Comodo run Rescue Disk

3. Click Options and you can choose whether to scan zips, the scanning level and so on

Comodo options

4. Choose the type of scan that you want and click it to start the PC clean-up task

Comodo scan disc

AVG Rescue CD

AVG’s free antivirus software is very popular and Rescue CD is basically the same scanning engine. It is an 85MB download and it boots up to a text-based menu with no mouse support. However, it is easy to navigate using the cursor keys, Tab and Enter. The program updates if there is an internet connection or updates can be loaded from disk or a USB drive if you save them beforehand. Download here.

It helpfully lists the disks attached to the PC, making files easy to find. There's a useful option to create a bootable USB flash drive. The Scan menu option scans the PC and repairs faults and malware infections. The Utilities menu has File Manager for exploring the PC’s disk, Registry Editor for fixing registry entries, Fix MBR for repairing the boot sector of hard drives when Windows won’t start, and PhotoRec and TestDisk for recovering lost and deleted files.

There's even a copy of TrueCrypt, which enables you to mount drives encrypted with the popular TrueCrypt utility. Some of the tools are awkward to use, such as the registry editor - we prefer Kaspersky’s.

AVG Rescue CD

AVG’s rescue disk has a text-based interface, but there are lots of useful tools

Kaspersky Rescue Disk 10

Kaspersky has built a much more comprehensive Linux-based rescue CD and this makes it a 263MB download. It doesn’t do any more than the others, but it's very easy to use and has a Windows-like interface.

You get the equivalent of a taskbar which shows running applications and a start button that pops up a menu. Multiple windows can be opened on the desktop and there is the Rescue Disk software itself, a registry editor, web browser and file manager. There are quite a few customisation options in Rescue Disk 10 and these are accessed through the gear icon in the top right corner. For example, you can choose what to scan and how deeply to scan. The registry editor is so like the Windows version you will immediately feel at home.

Kaspersky Rescue Disk 10

Kaspersky Rescue CD is nice to use and is perfect for novices because it’s Windows-like

Other rescue discs: