Can not format USB drive

[twpim-www@yahoo.com.au]

Hello,
I have a small USB disc (16G) that worked perfectly until now.
Now I am unable to perform any changes to this disc. No creating
new diroctories/files, no deleting, no formating ...

It has only one partition which formated as vfat filesystem.
Apparently it got some virus from Windows when it was plugged in that
machine. Originally I had four directories in root of this drive:
/dir_a /dir_b /dir_c /dir_d

After I unplugged it from Window box and plugged it my Debian box
I can see that some changes were made (by virus I guess):
- there is added file with name _111_.txt with size of 3 bytes
  containing ASCII text '111'

- for every directory that originally existed there is created new file
  such as: /dir_a.exe /dir_b.exe /dir_c.exe /dir_d.exe each with size
  516566 bytes

- on Windows box original folders are not visiable only newly created
  executable files are showed with icon as folders and without .exe extension

Maybe somebody can identify by this description which virus is this?

I can mount this drive in Debian box but only in read-only mode. It make
no difference if mounting as regular user or superuser:

# mount /dev/sda1
mount: block device /dev/sda1 is write-protected, mounting read-only

# umount /dev/sda1

When I try to format the partition on that disk (as superuser) I get
this error:
# mkdosfs /dev/sda1
mkdosfs 3.0.1 (23 Nov 2008)
mkdosfs: unable to open /dev/sda1

If I try to delete that partition any change I made is not saved:
# fdisk /dev/sda
You will not be able to write the partition table.

I even tried this with no success:
# dd if=/dev/zero of=/dev/sda
dd: opening `/dev/sda': Read-only file system

So for now I can not use that USB stick for anything.

Can you give me any advice how to repair that disc?

Thanks
Martin