Using the command line tool cipher.exe built into Windows 7, can it be used to securely wipe a USB attached drive?
You can also use sdelete from http://technet.microsoft.com/en-us/sysinternals/bb897443
Just commenting the answer given already (comments cannot be styled).
This is part of help printout for cipher.exe
Displays or alters the encryption of directories [files] on NTFS partitions. CIPHER /W:directory /W Removes data from available unused disk space on the entire volume. If this option is chosen, all other options are ignored. The directory specified can be anywhere in a local volume. If it is a mount point or points to a directory in another volume, the data on that volume will be removed.
Is this true that only NTFS file system can be "cipher-ed"?
What about FAT32 format which is used lately for UEFI compatibility?
Seems better to use special utilities for wiping.