In mod/turnitintool/lib.php there is a function called turnitintool_tempfile(). This contains a potential infinite loop..

The lines are...

    while(!$fp) {

        $file = $temp_dir.DIRECTORY_SEPARATOR.mt_rand().'.'.$suffix;

        $fp = @fopen($file, 'w');

    }

I assume the idea is that it loops if a filename clashes. However, this will loop "forever" if the fopen() fails for ANY reason. Something like a permission problem or a lack of disk space would be all that was needed. Worse - if something has gone wrong the @ prevents the admin ever finding out what the actual underlying error is.

This needs rewriting. Personally I would pick a random number and then increment it by one until a valid file was found by actually checking if the file exists. I think Moodle had a function for this somewhere but, of course, I can't find it now!