If you apply the update to a live web-server, there will be some period of time when the web-server will be offline (although an OS reboot should not be required). You’ll want to schedule and coordinate your updates appropriately.

Importantly – if your site or application is running across multiple web-servers in a web-farm, you’ll want to make sure the update is applied to all of the machines (and not just some of them). This is because the update changes the encryption/signing behavior of certain features in ASP.NET, and a mix of patched and un-patched servers will cause that encryption/signing behavior to be incompatible between them.  If you are using a web-farm topology, you might want to look at pulling half of the machines out of rotation, update them, and then swap the active and inactive machines (so that the updated machines are in rotation, and the non-updated ones are pulled from rotation and patched next) to avoid these mismatches.

Does this update work with SharePoint?

Yes.  We have not found any issues in testing SharePoint with this security update.  You should install it on SharePoint servers to ensure that they are not vulnerable.

Can I both install and uninstall the update?

Yes. The updates support install and uninstall scenarios.  Note that if you uninstall the update, though, it will leave your system unprotected.