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If the host operating system is Windows 7 and we suspect it being infected is it safe to run a LiveCD? Is it possible for the session in which the LiveCD runs to be come infected i.e. by trojans, viruses, etc that run in memory such as TDSS, etc?

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If you mount your local disk inside the LiveCD OS, so the OS can see the virus, if this virus takes the benefict of "be seeing" mechanism to infectate your current OS so it would be possible to get infected. However, I don't know any virus that do this. Also, remember that the virus must be to the plataform used by your LiveCD (Probabilly Linux). I think that you will be safe on using the LiveCD and will not have any problem with a infected host disk.

Also, the only think that could be infected by the virus is the OS that is already loaded and running on your RAM from the LiveCD(the current LiveCD instance), the LiveCD usually is read-only. So, if you suspects anything on your current OS instance, then reboot your LiveCD OS and keep the local disk unmounted.

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What do you mean by 'Also, remember that the virus must be to the plataform used by your LiveCD (Probabilly Linux)' – PeanutsMonkey Nov 22 '11 at 18:36
I mean that if the LiveCD OS is linux based, such as live Ubuntu, the virus on the local disc inside the host machine must infect the Linux... If you have a Windows 7 plataform inside the disk(infected by Windows based virus) and run a Linux LiveCD, the virus will not infectate the Linux OS running on RAM. – Diogo Nov 22 '11 at 18:44
Do LiveCDs automatically mount the local harddrive or disk? – PeanutsMonkey Nov 22 '11 at 19:23
This is a good question.... I dont usually use LiveCDs, but i will test it and post the results here. – Diogo Nov 22 '11 at 22:12
@PeanutsMonkey It depends on the distro, but Ubuntu liveCDs tend to mount the windows drives underneath. But... Windows viruses tend not to be cross platform, you can't 'run' anything windows on Ubuntu generally. So, you can see the virus code, but it can't run. – Rich Homolka Nov 22 '11 at 22:45
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up vote 6 down vote

Yes. It will be safe to run a LiveCD for two reasons:

  • The LiveCD is generally on read-only media.
  • Cross platform malware is extremely rare.
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So even if the system was infected with TDSS or Rustock, the LiveCD would be able to evade an infection? – PeanutsMonkey Nov 22 '11 at 18:32
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If you are using an actual cd-rom that was closed when you finished burning it. Then yes. – MrStatic Nov 22 '11 at 18:33
@MrStatic - I take it if I don't access or mount the harddrive, this limits infection. Do LiveCDs generally come with firewalls, antivirus, etc? – PeanutsMonkey Nov 22 '11 at 19:12
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up vote 4 down vote

It depends on exactly what you mean by safe. CD-ROMS are read only and even CD-Rs and CD-RWs often require special efforts (at least on the OS end of things) to write to more than once. So, it is generally impossible to infect a LiveCD, unless it was somehow infected at time of creation.

Now, the session can certainly become infected. But if you are careful about not running programs from the harddrive and only accessing data of types that you know is not infected you should be able to keep that risk very low indeed.

I have in the past booted off a known clean harddrive in order to pull essential data off a partially corrupted or infected drive before formatting the drive with some success, if that is what you are looking for.

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How do I know that the LiveCD is not infected? – PeanutsMonkey Nov 22 '11 at 18:34
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The short answer is that if you got the liveCD image from a reputable source and jus burned the ISO image onto a write-once CD-R, you can be fairly confident it is not infected. – TimothyAWiseman Nov 22 '11 at 20:52
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