How can I securely erase files from a USB drive, using Windows? [duplicate]

Possible Duplicate:
How to wipe a USB hard drive

[Author edit] Actually I think the duplicate is this one: Permanently delete files from a flash drive [/edit]

I have a USB stick returned to me by someone else. To maintain confidentiality of what it was used for I want to perform a secure erase on it so that data recovery tools cannot retrieve the contents - I don't know whether the same tools that are used for HDD's can be used on USB sticks, or whether a format will actually overwrite the existing (and deleted contents).

Is there a simple app that can perform this task? Freeware preferably.

CCleaner has an option to wipe free space on a drive.

Then there is also the free open source Eraser.

All of the other answers do provide ways to prevent the drive from being read using OS based recovery tools, however if the drive swapped out sectors due to bad sector errors/wear leveling (I doubt low end USB keys will do this but it is possible) the data could be recoverable by reading the flash memory chip directly and bypassing the controller.

See this answer from the security SE site for more details and read the Inaccessible media areas section on Wikipedia's "Data remanence" article. Once something has been written on any drive (flash/SSD/Spinning Disk) if you can not bypass the controller and write directly to the media (Even DBAN can not overwrite bad sectors) then you can not trust that the data is ever "gone".

I use DBAN or Eraser as mentioned above. Both are free and relatively easy to use.