A long time ago I found a hidden directory on my file server that some student had created to store their pirated software. This was back in the days of DOS and Novell NetWare.
Turns out you could create files with "illegal" (and invisible) characters in the filename. The standard OS utilities would not allow them, but the underlying file system did not care. So you could write a short program to do it.
They should have fixed that when they went to long file names. It's ridiculous that you can't name a file with its contents' actual title. Random example: http://doi.org/10.1145/327070.327153
Connecting from another operating system that allowed names like that to be corrected to a Windows share.
There are a few other possibilities where you boot to Linux using a FS driver for NTFS that allows you to create illegal file names. And/or odd things like WSL/Cygwin.
> < > ” / \ | ? * Never allowed
A friend once somehow crated a file called <HTML>.
I don't know how, but he also couldn't delete or do anything with it.