Visio 2013 drops support for writing VDX files in favor of the new VSDX and VSDM file formats,[12] and uses them by default. Created based on Open Packaging Conventions (OPC) standard (ISO 29500, Part 2), a VSDX or VSDM file consists of a group of XML files archived inside a Zip file.[12] VSDX and VSDM files differ only in that VSDM files may contain macros.[12] Since these files are susceptible to macro virus infection, the program enforces strict security on them.[14]