To format your "Ãusb", use dd:

dd if=/dev/zero of=/dev/sdx

change sdx to your interface.
If you are paranoid about your system being infected, you should reinstall your system and reflash your BIOS...
But since you don't know how to use dd to format a disk, you probably have many other security problems that doesn't include your friend's software. Encrypt your disk if you want more security/privacy.