***09-26-2017 UPDATE - We've confirmed that this issue has been resolved and you should no longer see the warning.***
Next time you update your Second Life Viewer on Windows there is a chance that you'll get a warning from Windows Defender SmartScreen that looks something like:
Assuming you got the installer by downloading from our web site or through an automatic viewer update, you can safely tell it to "Run anyway".
What's happening? When you launch something that's been download from the Net, Windows checks with Microsoft to see whether or not the thing you're launching is ok. When the answer is effectively "we're not sure," that warning is displayed.
Normally, we don't get these warnings because for many years we've been digitally signing the viewer and its installer and Microsoft has been recording the fact that things signed by us have been installed many times by many users. Unfortunately, what Microsoft uses to recognize that the application is from Linden Lab is the code signing key we used to generate the signatures. That key expired this week, and we had to get a new one. Until enough people install the application signed by that new key, it won't have a good enough "reputation" with Microsoft to avoid the warning.
So please help out your fellow Windows users (and us :-) ) and install those updates so that our new key develops the same well-trusted reputation the retired one had.