The FileAPI accepts files with filenames that contain characters which are illegal in some operating systems. This can cause issues when those files are created in a OS where the filename is legal, then downloaded to one where they are illegal.

Example:
A student using MacOSX creates a file and saves it as

 assignment_*NEW*_#2.docx 

. Student submits this file on a assignment module attempt.

A teacher using Windows Vista opens assignment module and selects "Download all submissions". The submission

 assignment_*NEW*_#2.docx 

is not displayed because it contains illegal characters in its filename.

Suggestion:
Clean filenames to strip characters / ? < > \ : * | " when a file is saved.

Additional note: we will also need to strip ';' from the filename as recent tests showed that this was causing issues down the line (see MDL-79016)