The MIME types “text/plain” and “application/octet-stream” are termed ambiguous because they generally do not provide clear indications of which application or CLSID should be associated as the content handler…
…and defaulting to the final determined MIME type of “application/octet-stream.” Other types of files, such as .reg files, behave similarly.
Finally, if no file name extension is found, or one is found with no associated MIME type or registered application, the MIME type “text/plain” is returned if the data scan indicated predominantly text, or “application/octet-stream” if the data scan indicated binary, because this is the furthest correct determination that could be made.