The .NET Framework 4.5 is a highly compatible, in-place update to the .NET Framework 4. By using the .NET Framework 4.5 together with the C#, Visual Basic, or F# programming language, you can write Windows apps. The .NET Framework 4.5 includes significant language and framework enhancements for C#, Visual Basic, and F# (so that you can more easily write asynchronous code), the blending of control flow in synchronous code, a responsive UI, and web app scalability . The .NET Framework 4.5 adds substantial improvements to other functional areas such as ASP.NET, Managed Extensibility Framework, Windows Communication Foundation, Windows Workflow Foundation, and Windows Identity Foundation. The .NET Framework 4.5 delivers better performance, reliability, and security.
For more information about these and other features of the .NET Framework 4.5, see the .NET Framework Developer Center website.
Note: The .NET Framework 4.5 redistributable was updated on 10/9/2012 to correct an issue related to an improper timestamp on a digital certificate which causes the digital signature on files produced and signed by Microsoft to expire prematurely. We recommend customers that previously installed the .NET 4.5 redistributable package dated 8/16/2012 install this updated .NET 4.5 redistributable package. More information about the issue can be found Microsoft Security Advisory 2749655.