Windows Metafile (wmf ) is an image format originally designed for Microsoft Windows in the 1990s, intended to be portable between applications and may contain both vector graphics and bitmap components, acting somewhat similar to svg files.

Essentially, a WMF file stores a list of function calls that have to be issued to the Windows Graphics Device Interface (GDI) layer to display an image on screen. Since some GDI functions accept pointers to callback functions for error handling, a WMF file may erroneously include executable code.