IF YOU think money can't buy you friends, think again. In the online world, it’s possible to purchase a crowd of fans. One thousand cost only $18 on average, according to estimates by Barracuda Networks, a network security company. Yet these friends won’t meet you for drinks after work. In fact, they don’t even exist. They are pixels on a screen. A large share of social-media followers of the biggest companies are not human, believes Marco Camisani Calzolari, an entrepreneur and professor at Milan’s ILUM University. In a recent study he quantified the proportion of computer-generated fans or inactive users following big brands on Twitter. To decide whether a follower is human, Mr Camisani Calzolari used various criteria, including the number of posts from a fan’s Twitter account and the use of correct punctuation in tweets. According to this research, by June 2011 nearly half of Twitter followers of computer maker Dell—about 700,000—were bots. Some politicians also seem to have many fake followers. Mitt Romney, the former Republican presidential candidate, became the focus of media attention when his Twitter following swelled by 17% in a single day in July. On close inspection, a significant proportion of Mr Romney’s followers appeared to be fake profiles. In Italy Beppe Grillo’s Five Star Movement lost momentum when Mr Camisani Calzolari made a similar claim about the followers of the comedian-turned-politician. There is no indication that any of the companies mentioned in Mr Camisani Calzolari’s paper have bought followers—rogue bots often attach themselves to people and brands without payment. But some firms do buy a social media following. Fake profiles are at the centre of a very vibrant and growing underground economy, says Barracuda Networks. On eBay, the e-commerce site, for instance, the firm’s researchers have found 20 sellers offering to set up such profiles.

For start-ups a strong social media following can boost business. A small mom-and-pop shop struggling to sell its wares can look like a booming upstart thanks to a swollen Twitter account, or an artificially high number of Facebook likes. For major international companies, an underwhelming number of followers in the early stages of engagement with social media can be galling at best and damaging to brand perception at worst. Buying crowds of fans—even if they aren’t engaged with the brand—can give an artificial boost to a business.

For now, the trick works. “Normal people don't know yet that there is this black market. Most have total trust that a brand's followers are real,” says Mr Camisani Calzolari. But brands are already finding diminishing returns. When everybody has a large following, the impact is much diminished. And consumers are starting to cotton on to sharp practices. “The number of followers is a superficial measurement unless they are engaged,” argues Carly Donovan of Ogilvy Action, an arm of Ogilvy & Mather, the advertisement and public relations agency. Money can buy you friends—just not very good ones.

P.S.: In the interest of full disclosure, 13% of the more than 325,000 accounts that follow The Economist’s business and finance channel on Twitter (@EconBizFin) are fake, at least according to StatusPeople’s Fakers app, which claims to be able to calculate such numbers.