.NET AppDomains provide several levels of isolation for untrusted or partially trusted code. The AppDomain sandbox is widely deployed in ASP.NET and Silverlight, although only the latter of these is designed to isolate completely untrusted code from the rest of the OS.
Have there been any known escapes of AppDomain-based sandboxes? I was unable to find any security advisories related to this in a cursory search. Of course this doesn't mean the sandbox is secure; it could simply be little-used. But it's a start.
I'm asking because the documentation from MSDN as to whether the sandbox is to be relied on appears to be contradictory. There's this page which states "we advise against loading and executing code of unknown origins without putting alternative security measures in place". And then there's this article whose entire title is "How to Safely Host Untrusted Add-Ins".