Social media marketing has been a major trend among marketing professionals for the past five years. It exploits the ability of social media to reach extremely precise target audiences on the basis of the massive data that social network users themselves provide. Thus rather than ads often being off target (e.g. women receiving spam for Viagra and men seeing ads for feminine hygiene products), Facebook ads can be made narrowly relevant to users, exploiting knowledge of organization memberships, habits, favourite media personalities, etc. Facebook advertisers also use "likes" and the mechanisms of being able to reveal your friends' preferences to exploit a herd mentality, taking advantage of the fact that the more people in your network buy or follow a product, the more likely you will be to buy it. Often they trade free samples or discounts for "likes" or "follows" to exploit this effect.