Last year I blogged regarding the end of support for .Net Frameworks (4, 4,5 & 4.5.1), starting January 12, 2016 and it’s not far away – please there will be no longer provide security updates, technical support or hotfixes for .NET 4, 4.5, and 4.5.1 frameworks. All other framework versions, including 3.5, 4.5.2, 4.6 and 4.6.1, will be supported for the duration of their established lifecycle.
It matters a lot – refer my earlier blog post and just make sure that you use a supported version of the .NET Framework is installed in your environment, on Windows desktops and servers; it includes Azure and other cloud service deployments. You can use the article to find out “How to determine which .Net Framework versions installed at your computer”. Refer @ https://msdn.microsoft.com/en-us/library/hh925568(v=vs.110).aspx. In addition, you can refer my related blog post http://blogs.msdn.com/b/deva/archive/2015/12/22/ok-now-how-to-find-net-version-installed-in-any-given-environment.aspx as well.
Detailed info is available at DotNet Blog post - http://blogs.msdn.com/b/dotnet/archive/2015/12/09/support-ending-for-the-net-framework-4-4-5-and-4-5-1.aspx. It includes interesting info (refer the below snapshot) for products like Exchange, SharePoint, Lync/Dynamics etc. For more details on the .NET Framework support lifecycle, visit the Microsoft .NET Framework Support Lifecycle Policy FAQ. Additionally, compatibility of the .NET framework can be viewed on the .NET Application Compatibility page.
Hope this helps.