If your Pen Drive is infected with any of the following viruses

* Autorun.inf
* new folder.exe
* Iexplorer.vbs
* Bha.vbs
* nfo.exe
* New_Folder.exe
* ravmon.exe
* RVHost.exe or any other files with extension.

These viruses are hidden nd can't be seen even if you click on "show hidden files and folders"

So follow these simple dos command and change the attributes of these files ,there after you can remove it by pressing delete
key.

Follow these steps:
Step1.:Type cmd in Run
Step2.: Switch to the drive on which pen drive is connected
(like C:\> h: enter)
Step3.: type exactly as attrib -s -h *.* /s /d and hit enter
(don't forget spaces).
Now you can see hidden virus files and you can delete them.