"Dangerous" copyleft licenses are separated ...

"This is the top level of the FreeBSD source directory.  This file
was last revised on:
$FreeBSD$

For copyright information, please see the file COPYRIGHT in this
directory (additional copyright information also exists for some
sources in this tree - please see the specific source directories for
more information).
[...]
Source Roadmap:
---------------

bin        System/user commands.
cddl       Various commands and libraries under the Common Development
           and Distribution License.
contrib    Packages contributed by 3rd parties.
crypto     Cryptography stuff (see crypto/README).
[...]
gnu        Various commands and libraries under the GNU Public License.
           Please see gnu/COPYING* for more information."
[...]
secure     Cryptographic libraries and commands.
share      Shared resources.
sys        Kernel sources."
/usr/src/README (redacted)

Proprietary software may be anywhere, though.
Happy hunting!