Using Linux to scan and remove viruses from a Windows computer

A common problem with viruses is that they are often extremely difficult to remove. Most of the time, you easily understand that there is something strange about your Windows box (apart from the usual Windows behaviour, that is :D) , so you run a virus scan and indeed, confirm your worry that you have been infected. But what is the worth of your antivirus application if it is unable to remove the virus, not to mention detect it in the first place?! Often, you need to find a dedicated mini-application that removes a particular virus, but if you can't, you're screwed.

The following is a recipe that works:
1. Install Ubuntu 8.04 (Hardy Heron) Persistent on a USB stick (see this guide, and read my reasons why)
2.Install antivirus applications on the Ubuntu system on the USB stick.

• Avast Antivirus is easy to install (.deb available) and is free but requires email registration for a key (no spam).
  
• Clam Antivirus is free and also available from repositories (enable universe). If you prefer a graphical user interface (GUI), also install clamtk using Synaptic.
  
• AVG Anti-Virus Free for Linux/Freebsd 7.5.50 is not their latest release but might do the job.
  
• Trend Micro HouseCall is a free online scanning service. Linux distributions must support libc6.

3. Make sure the antivirus applications and virus definitions are all updated.
4. Boot up Ubuntu on the infected Windows computer using your USB stick. You may have to enter the BIOS setup to change the boot order to boot from USB before booting from the (Windows) hard drive.
5. Launch an antivirus application in Ubuntu and tell it to scan the directory /media, where the windows partitions shall have been automounted as /media/disk, /media/disk-1, etc. at boot time.

(Note: I have only tried Avast and Clam. I noted that Clam seemed to be unresponsive upon starting a scan, but after 30 seconds or so started scanning.)

When you have successfully cleaned your mom's/dad's/friend's computer, lend them your USB stick (with all the usual snacks like Compiz Fusion/the 3D cube, OpenOffice, Opera 9.5 with email set up, Amarok, VLC player etc.) and tell them that anything they can accomplish in Windows (well, perhaps with the exception of premium video editing suites such as Adobe Premiere Pro) they can do with free software in a virusfree Linux environment!

Why you should install Ubuntu 8.04 (Hardy Heron) Persistent on a USB stick

There are several reasons you should install Ubuntu on a USB flash drive. First of all, a USB memory stick is easier to bring around than a Live CD if you need to install Ubuntu on a computer. But more importantly, by installing the persistent version, not only can you use your USB as a Live CD, but in addition, you can save any changes to the system to disk! In effect, this means that you have your own portable system that you can bring anywhere. Forget the worry of bringing your valuable laptop on vacation. Instead, once you have booted your system onto somebody else's computer, you can install software, perform system upgrades, and do your work on your own customized system with your own software installed. Everything you do is saved onto your USB stick. And if you do need to access or save something on the underlying system, the computer hard drives will be automounted at startup.

Naturally, your system will be limited by the disk size of your USB. Most installations use about 700 MB (the size of a Live CD) for the Live portion of the system, leaving the rest of the disk as free space. With a dirt-cheap 4 or 8 GB USB stick, you have plenty of space to install software and files.

Running a system from a USB can also be convenient if you need dedicated servers to perform exactly what you want. Rather than going through a procedure of installing necessary software and making sure that everything works on the existing system, which likely is a Windows computer loaded with crap, you simply plug in your pre-prepared USB stick and boot from it. It is cheap and quick to buy 10 USB sticks, prepare the system and software on one of them, and then replicate the entire system onto the 9 others.

Another great usage is for removal of viruses on a Windows system. Viruses are often hard to get rid of, as they might get loaded during boot-up and refuse to be deleted by the Windows antivirus application. Booting Ubuntu from the USB and running a virus scanner such as Avast or Clam (Clam is also available from repositories) should enable you to remove the viruses. See my guide for further instructions.

So how do you make such a USB stick? I just followed this guide, which was a piece of cake. If you want the USB stick to also work as a normal flash drive when connected to a computer, you might want to add a third partition in addition to the two needed for the Ubuntu Persistent system. Format it as NTFS so it is readable on both Windows and Linux systems. You might need to have this partition as the first partition for Windows to discover it. I have not tried this myself, but believe it should work.