AVIRA offers Avira Rescue System, which you can use to start and scan your computer.

You have to burn the Rescue System on a CD, in order to boot your PC from the Rescue CD.

However, there are computers (e.g. Netbooks) without an optical drive. In this case, you can use a re-writable medium (e.g. USB stick) to boot from.

Here is how you start Avira Rescue System from the USB stick:

1. Download Avira Rescue System as .iso file from the following URL:
   Avira Rescue System
2. Download the program "Unetbootin" from the following URL:
   Unetbootin
3. Plug in the USB stick and format it.
4. Click Diskimage and select the .iso file you have just downloaded.
5. The USB drive should be selected under "Type".
   Please make sure, that the correct USB stick is selected, under "Drive"
   
   
6. Press OK. The files are copied and the bootable USB is created.
   
   
7. Now you can boot your PC from this USB stick.
   
   

Note: You do not have to download a new .iso file every time. If you have an Internet connection, you can easily update Avira Rescue System.