A fifth of your Facebook friends are people you don’t even know—and three-fifths are just acquaintances, a study finds. The fact that only 20% of your friends are your actual friends may not come as a surprise to the average Facebook user, notes AllFacebook.com, but it’s a fact worth remembering: After all, the more unfamiliar friends you have, the greater your risk of getting malware and spam. Why keep so many so-called friends? 54% of responders to the survey, conducted by GoodMobilePhones, cited politeness, while 34% said they wanted to look more popular. (More Facebook stories.)