Facebook has launched an ambitious program to remove phony likes. Indeed, a substantial percentage of likes on the site are dubious, experts say. The trick for the social network is to delete false ones without doing away with legitimate likes, which would alienate members and advertisers.

False likes are often placed by phony accounts set up to pimp like-hungry brands or by bots that hijack a legitimate account. Facebook can profit from them, since high numbers of likes encourage ad buyers to spend money on the site, but illegitimate likes also cast doubt among investors that the company can deliver stable growth. Facebook is attacking the problem at a time when stakes are growing to deliver likes to a brand.

Facebook declined to discuss how it is eliminating fake likes, for fear of tipping off spammers. Its method likely hinges on pattern recognition. “Facebook has access to a lot of data," said Chris Weber, cofounder of the cybersecurity firm Casaba. "They can recognize a great number of patterns, and can very likely use behavioral statistics to qualify what activity looks normal and real versus what activity that looks fake or automated.” 

Facebook has announced that the program is likely to eliminate no more than 1% of likes on any given page. However, it could axe as much as 25% of likes, according to Tom Corson-Knowles, an online marketer who consults with small-business owners on ways to promote products on social networks. Corson-Knowles bases his estimate on his contacts with thousands of so-called virtual assistants - essentially freelance social marketers - who typically offer clients 1,000 likes for about $25. 

"One thing all of these virtual assistants have in common is a large number of fake profiles that they use,” he said. “The average virtual assistant I've seen who does Facebook marketing has at least five Facebook accounts.”

Such deals have proven irresistible to marketers. “Business owners jump on the chance" to get hundreds of likes, said Jayme Pretzloff, online marketing director for Minneapolis-based Wixon Jewelers, "but they don't realize the repercussions of doing this. Facebook has already cracked down on this by changing its Newsfeed rankings based on engagement." Companies' strong engagement with their fans will appear more often in their fans' feeds, he adds.

Any cleanup must be exacting. A central concern of this effort is that Facebook participants will react angrily to the deletion of likes that they have placed. On Thursday morning, Facebook issued a statement saying it had received no reports of legitimate likes being removed.

But eliminating likes at all is perilous because they are essential to attracting advertiser dollars. “It's not in Facebook's best interest to proactively solve this problem," Corson-Knowles said. "Facebook's revenue is directly proportionate to the number of page views the site gets, and banning 1 percent of users who are deemed bots will cost the company a lot of missed ad impressions."