WITH A FEW VISITORS in the house for the Christmas season, I have to remember to log out of Facebook on my laptop, phones and iPad. This is important because one of my "friends" modified my profile picture when he discovered Facebook was live and accepting updates as he borrowed my laptop. Another "friend" created a status that only a small group of other people could see. The status message divulged something about a piece of lingerie belonging to a woman who was very concerned about a private party in someone else's flat. When she logged on, she could see a post in her newsfeed with embarrassing details and it created a lot of trauma. If you're feeling devious this holiday season and you discover an open log-in, you could also drive someone crazy with a Facebook post too. Just remember that before you post the message, click the lock icon next to "Share" and select "Custom Edit". Then set the post so it becomes visible only to "Friends of friends". And to wind up the unsuspecting victim, find the field called "These people" and pick the friend with whom you wish to share special joy. But don't expect much joy in return.