I have single partition of 92GB in which I installed Ubuntu 12.04. And for some Unknown reason a message pop ups saying that I only have 1GB of HDD space left.

I ran command sudo du -hscx * on / and /home

/home gave me this result

4.0K    C:\nppdf32Log\debuglog.txt
0           convertedvideo.avi
176M    Desktop
16K         Documents
169M    Downloads
4.0K    examples.desktop
17M         file.txt
4.0K    Music
984K    Pictures
4.0K    Public
320K    Red Hat 6.iso
2.5M    syslog-ng_3.3.6.tar.gz
4.0K    Templates
8.0K    terminal.png
1.2M    Thunderbird Attachments
698M    ubuntu10.04LTS.iso
16K         Ubuntu One
4.0K    Untitled Folder
4.0K    Videos
21G         VirtualBox VMs
22G         total

And / gave me this result

81G         home
0           initrd.img
0           initrd.img.old
833M    lib
16K         lost+found
68K         media
4.0K    mnt
260M    opt
du:         cannot access `proc/8339/task/8339/fd/4': No such file or directory
du:         cannot access `proc/8339/task/8339/fdinfo/4': No such file or directory
du:         cannot access `proc/8339/fd/4': No such file or directory
du:         cannot access `proc/8339/fdinfo/4': No such file or directory
0           proc
640K    root
908K    run
8.6M    sbin
4.0K    selinux
4.0K    srv
0           sys
148K    tmp
3.3G    usr
436M    var
0           vmlinuz
0           vmlinuz.old
86G         total

If you look at the result returned by / it shows that /home is consuming 81GB but on the other hand /home returns only 22GB.

I cant figure out whats consuming the HDD. I have not installed anything except Virtual Machines

Perpetrator found using Disk Usage Analyzer