i think several problems…

  1. you were infected by a “System Volume Information” Virus, so the numbers were wrong(?)
  2. [s]there was still unallocated data space left/s
  3. any other drives attached? usb drive maybe? external harddrive?
  4. what’s the current capacity of you harddrive?
    why did you do a boot-scan?
    what OS are you using?
    what version of avast are you using?