YOUR SISTER NAKED is a new version of a virus spreading via Skype in fact it is the same parasite as YOUR MOTHER NAKED hahahaha.pif. Usually it comes as a download from your Skype friend. If you already downloaded it you must delete it immediately. Once activated it is running in background and sending itself to all contacts from your Skype friends list without your permission. So simply you are infecting your friend with it. Also YOUR SISTER NAKED is able to download some additional malware to your computer. To avoid all possible problems we highly recommend you to use anti-spyware program.