"If someone steals a CD containing a version of a GPL-covered program, does the GPL give the thief the right to redistribute that version?" The answer is somewhat complicated. Read the full answer at https://u.fsf.org/3kv#GNUGPLFAQ
@fsf Today I Learned: You can license a particular version of your software's source code under the GPL but not release it to anyone for use outside of your home/company, and even keep it protected as a "trade secret." As long as no one but you/your company are using it, you do not have to share the code at all, this does not violate the GPL. However once you have published the code and allowed others to copy it, the GPL license requires that you allow anyone who happens to have obtained a legal a copy of that version of the source code (not including leaked or stolen code) to freely redistribute it or any modifications of it they make.