The security risks from this code appear to be low. Microsoft do appear to be checking for buffer overruns in the obvious places. The amount of networking code here is small enough for Microsoft to easily check for any vulnerabilities that might be revealed: it’s the big applications that pose more of a risk. This code is also nearly four years old: any obvious problems should be patched by now.
Microsoft’s fears that this code will be pirated by its competitors also seem largely unfounded. With application code this would be a risk, but it’s hard to see Microsoft’s operating system competitors taking advantage of it. Neither Apple nor Linux are in a much of position to steal code and get away with it, even if it was useful to them.
In short, there is nothing really surprising in this leak. Microsoft does not steal open-source code. Their older code is flaky, their modern code excellent. Their programmers are skilled and enthusiastic. Problems are generally due to a trade-off of current quality against vast hardware, software and backward compatibility.
I was also gratified to see this comment, based on a book I loved as a kid:
// TERRIBLE HORRIBLE NO GOOD VERY BAD HACK
Even in Australia…