USB Virus,"unformats" your Usb Drive....

Hey everybody,

I´ve got something weird happening over here.... I put my 4Gb usb pen drive in my colleague´s computer and everything seemed ok, but then I put my usb pen drive into my own computer and I got the message that it has no format. After a long time trying to figure out how to get my stored files back I gave up an d formatted the drive and before and after formatting my usb pen drive had tuned into a 27Mb drive.... I scanned my computer and my colleague´s computer with AVG 9.0.663 and Avast Home and found nothing.

Is there anybody out there who knows the answer of how to solve this mystery or at least someone who can tell me what it is? This mystery has cost me a 4Gb and a 16Gb pen drive and we are not able to run our daily backups to our external hard drive.

Thanks.