There are 2 file types use the .MSO file extension:
1. Microsoft Office Macro Reference File
An MSO file is a macro reference file created when saving a Microsoft Office document as a webpage. It contains information about macros and OLE (Object Linking and Embedding) objects included in the original file and may be referenced by the created webpage as a style sheet. MSO files may be viewed with a text editor, but will be unreadable since the contents are encoded.
Most users will only see the MSO file as an attachment to an email. Do not open the file if it has the ".mso" extension because it most likely contains a virus that will be installed on your computer when opened.
|Should not be opened manually|
Updated: June 9, 2016
2. Inline E-mail Attachment
File sent with Microsoft Word 2000 e-mail attachments; often named "Oledata.mso;" contains information that allows the attachment to be rendered within the e-mail message.
The Oledata.mso file will appear as a separate attachment on computers that do not have Microsoft Outlook 2000 or later installed.
Updated: June 22, 2008