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#### 11.1.1 Package Locking Overview

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.