The project homepage explains:
http://sourceforge.net/p/libusb-win32/wiki/Home/

 License

* The library (DLL and import lib, examples, installers) is distributed under the terms of the GNU Lesser General Public License (LGPL http://www.gnu.org/licenses/licenses.html#LGPL). Take note the installers in the older versions of libusb-win32 (before 1.2.0.0) is distributed under GPL, not LGPL.

* The driver portion (libusb0.sys) is distributed under the terms of the GNU General Public License (GPL http://www.gnu.org/licenses/licenses.html#GPL).

* This license combination explicitly allows the use of this library in commercial, non-Open-Source applications. Read the licenses carefully and apply all of their requirements before including this library in a commercial application!

* In the future the project administrators will add a New BSD option to the license to address the WHQL Licensing issue.
