Package locks protect against unintentional modifications of a
package: they provide similar protection to user packages as is
mandated to common-lisp
package by the ANSI specification. They
are not, and should not be used as a security measure.
Newly created packages are by default unlocked (see the :lock
option to defpackage
).
The package common-lisp
and SBCL internal implementation
packages are locked by default, including sb-ext
.
It may be beneficial to lock common-lisp-user
as well, to
ensure that various libraries don't pollute it without asking,
but this is not currently done by default.