Evil and useless license Microsoft
is pushing and trying to claim is the same as Open Source
. Since you can't do anything with the source except look at it and possibly send bug fixes back to Microsoft, you really have not gained much, and you are now tainted and may not be able to work on other software projects (including commercial and closed software, not just Open Source!)
This license is used on the larger and more secretive things Microsoft has huge contracts signed for, such as the source for WinCE. You don't have to worry about encountering it in code downloaded from the web, because that would be a code leak, there is no way you could agree to the restrictions of Shared Source without signing a contract and Microsoft signing it, too.
Not to be confused with the CPL that a few pieces of source code have been released under from Microsoft. That is apparently a legitimate and for-real effort to let people use and learn from their work.