Another word for - author unknown?

Here are some synonyms for "author unknown," depending on the context:

Formal:

* Anonymous

* Unattributed

* Ascribed to no one

* Of uncertain authorship

* Of unknown origin

Informal:

* No name attached

* No one knows who wrote it

* Mystery writer

* Secret author

The best option will depend on the specific situation and the tone you want to convey.