Microsoft programmers are forbidden to read open source code?

While searching for a solution to the problem, on the Apple developer mailing lists I came across an interesting email :

On 12/29/07 12:42 PM, “Steve Peters” <email @ hidden> wrote:

<snip />

> For the answer to this question and the kernel
> source at
> < www.opensource.apple.com/darwinsource/10.5/xnu-1228 >
>
> SCP
')
Alas, this resource is not available to us Microsoft employees. Our
corporate policy prohibits the reading of open source code (that isn't
ours), because it avoids ip taint into our
commercial products **. We're limited to reading plain old documentation, so
if you have pointers to that, we'd appreciate it.

-nh

* Strictly speaking, we could theoretically infringe by implementing
something that’s a pre-existing patent, but this way, our
exposure is significantly limited.

- Nathan Herring
CoreCLR SDE / Development

In principle, everything is logical: programmers from Microsoft are not allowed to read other people's open-source code so that they do not accidentally include it in their programs, because in the case of GPL code, you have to open all the source code of the program.