On the one hand, social-networking sites are awesome. They allow you to connect with friends, share pictures and memories, and let your presence on the Internet be known. On the other, social networking gives way to a handful of creepy situations: one of them being lurkers. Lurkers are essentially creepers who stalk down your Facebook so they can constantly be on top of what you're doing. It's not always easy to spot a Facebook lurker, but if you do, there are many precautions you can take: delete them, block them, make your profile private, etc. Here are the 15 Ways to Know Someone is Lurking on Your Facebook.