User information file created by Visual Studio 2013, a software development tool used for creating Windows programs and Web applications; structured in a binary format; stores user information such as opened tool windows, start-up project details, user tasks, and opened files.

When you closed a project and reopen it, all of your opened files, position of windows, and other details remain the same because of the information contained in the V12.SUO file. The file is referenced by VSPackages created with Visual Studio, opened by the LoadUserOptions Method, and modified by the WriteUserOptions and SaveUserOptions methods. The compound extension ascends with each new version of Visual Studio. Visual Studio 2012 uses the .V11.SUO extension. NOTE: If the V12.SUO file becomes too large, it can be deleted to boost Visual Studio's performance. However, if you delete it you will lose the user-specific data contained in the file.