You might want to read the GNU General License that Linux is written and distributed under. If Google is using Linux, they can't make the code private. It has to stay open source.
That license means that:
...any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all.In light of this, you may want to rephrase your comment.
No problem. Here's my rephrase:
Google publishes most of it's code under an Open Source license as defined by the Open Source Initiative.
Most Google code is published under the Simplified BSD License which does allow the code to be used in a closed-source project.
Many of the Google-sponsored projects in the Google Summer of Code (and the changes made to Linux for things like the GoogleOS) are licensed under the GPL.
Better?
If Google is distributing linux, they have to release the source code.
They do use linux, but AFAIK they haven't released the modifications.