This search term can be used to search for files with no extension, for example
when it should be
The search term is not perfect, as it brings up other abnormalities such as ._filename.zip or filename.zip<space> or filename.zip 2 – but it does a good job still and these abnormalities are things that should also be check.
ext: NOT kind:folder
To use, simply browse to the root level folder that you want to search and enter the search term into the search box.