A virus typically used to steal credit card information has been repurposed to target Instagram, generating fake "likes" and followers, and selling them online. As Reuters reports, these fake "likes" are then sold in batches of 1,000 on online forums, and can fetch surprisingly high prices. According to security firm RSA, 1,000 Instagram followers sell for around $15 online, while 1,000 "likes" selling for $30. The same number of credit card numbers, by comparison, go for as little as $6.

Experts say this price discrepancy reflects the growing value of social media to businesses or individuals who want to promote their brands or products. Buying fake likes is an easy — if ethically nebulous — way to generate false hype around a brand, and companies are clearly willing to pay comparatively high prices for them.

"It's fine for the first 100, but I advise stopping after that."

The malware, known as Zeus, first surfaced in 2007 as a botnet network to steal banking and credit card information, and has infected millions of computers. In its modified form, the virus forces infected users to follow or like specific accounts, or to download other viruses. It's not clear how many people have been targeted by the latest version of Zeus, but experts tell Reuters that it's the first malware created explicitly to generate fake "likes" on social media.

Online marketers say they sometimes advise clients to purchase social media followers to kickstart their campaigns, though relying too heavily on false buzz can soon backfire, making the brand look cheap or spammy. "It's fine to do for the first 100 [followers]," Will Mitchell, an online marketing consultant, told Reuters. "But I always advise stopping after that."