Say I deploy a .NET application, and Microsoft issues an update or a hotfix that changes the behavior of the .NET layer. Could this affect the predictability of my code, causing it to behave in an unintended manner, if my code is relying on some specific output or side effect of a given .NET method or component?
And can I force my code to use a certain version/build of the .NET layer so that if my customer updates his .NET layer, my code continues to use the old one?
Am I being paranoid or is this a legitimate concern regarding something that has happened in the past?
Yes, key hotfixes have been known to effect programmes, not just .NET. That being said the likelyhood is really low, hotfixes might stop a non-standard or hacker approach, but won’t touch the mainstream stuff. Build a unit-test suite, and test your code as you get each KB – release patches if you find something’s failed (which you probably never will, but you’ll have peace of mind :)).