Vidmar uses software to follow tens of thousands

In April, Twitter and the researchers applied the filter. Mr. Vidmar says he remembers the day, because most of his fake accounts were deleted, and he couldn't create new ones. "They cleaned house," he says.But Mr. Vidmar and others say the underground market quickly adapted. The researchers' system flagged accounts with incomplete profiles, no pictures, and little activity. In response, Mr. Vidmar says suppliers now fill out more account details, add pictures, and tweet from the accounts before selling them.That drove up the cost of fake accounts. But marketers and researchers say the black market is again thriving.Just two weeks after the crackdown, Twitter caught only about half the suspicious accounts being offered by merchants previously identified as selling fake accounts, according to the Berkeley researchers.

Mr. Vidmar says one of his suppliers is offering 150,000 fake accounts for sale. "I could go buy fake accounts from about 20 different sources right now," he says.Mr. Ding, the Barracuda Labs researcher, says the fake-account market is "going very strong." He and other researchers say Twitter doesn't appear to be applying the Berkeley researchers' techniques to root out other fake accounts.Mr. Vidmar's robots have helped make his clients "trending topics" on Twitter, giving them special mention on Twitter users' home pages. The trending topics appear just below the "promoted trend" that the company sells for as much as $200,000 a day. The trending topics aren't marked as "sponsored," so they appear more genuine.

Rapper Tony Benson says hiring Mr. Vidmar to promote his account on Twitter is "the best decision I ever made." Mr. Vidmar's robots made the rapper, known as Philly Chase, a trending topic so often around Philadelphia that he attracted attention from local newspapers. Prominence on Twitter led to gigs, fans and ways to promote his videos, Mr. Benson says.Mr. Vidmar uses software to follow tens of thousands of accounts for his clients, another tactic Twitter prohibits. Being followed prompts many Twitter users to return the favor, and follow his clients.In September, Mr. Vidmar used software to follow more than 100,000 Twitter users in a week for the Australian rock band The Contagious; that boosted the band's following by 20,000.