Using .NET 4, 4.5, 4.5.1? Only 4.5.2 will be receiving technical support and security updates after Jan 12, 2016 (so start your 4.5.2 planning/deployment...)
The quick pace at which we’re evolving and shipping means the latest fixes, features, and innovations are available in the latest version and not in legacy versions. To that end, we are making it easier than ever before for customers to stay current on the .NET Framework 4.x family of products with highly compatible, in-place updates for the .NET 4.x family.
We will continue to fully support .NET 4, .NET 4.5, .NET 4.5.1, and .NET 4.5.2 until January 12, 2016, this includes security updates as well as non-security technical support and hotfixes. Beginning January 12, 2016 only .NET Framework 4.5.2 will continue receiving technical support and security updates. There is no change to the support timelines for any other .NET Framework version, including .NET 3.5 SP1, which will continue to be supported for the duration of the operating system lifecycle. [GD: Emphasis added]
We will continue to focus on .NET and as we outlined at both TechEd NA and Build earlier in 2014, we are working on a significant set of technologies, features and scenarios that will be part of .NET vNext, our next major release of the .NET Framework coming in 2015.
Pretty clear, start moving to .Net 4.5.2 soon. No, the world will not end, but still being on a "supported" .NET version is pretty darn important.
BTW, did you catch the .NET vNext coming is in 2015? Nice to see that in print... :)