Downloaded the windows client today, did a few searches, found the Short, insecure "secrets" thread, and the cats secret (R27WAH4LQCGDFOGS7NLQYLQPXW5TRCW5) which I put in a New Folder on my desktop. After an hour or two of downloading, lots of cat pictures, I noticed a folder called "Hello" being created and deleted on my desktop. It didn't contain anything but it's very presence indicates a glitch that allows somebody to create/delete files/folders one directory higher than the one they're linked to. Is this the security issue OP describes? I have shut down and uninstalled Sync.