I've just upgraded a site from static html to dynamic php with a custom CMS system. Just now I've just noticed that i've got some wierd files in my ftp root folder.
Two are core.**** (*s = numbers) files (each 36.9MB!)
One is called ".pureftpd-upload.4600388e.15.4402.2f61c688" which refuses to be deleted (or even renamed) because of a "550 Prohibited file name" error