Despite what was reported on the vBulletin.com thread there is indeed code in vBulletin 3.x to create those files.
In 3.8.7 it starts on line 271 of class_upload.php and also line 341 of class_vurl.php.
It looks like the guy who said it has something to do with the php temp directory was correct- my guess it's a result of a server without a working php temp directory defined- or some other temp directory issue.
But it looks like they can safely be deleted- especially the 0 byte ones.
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