According to Facebook management software vendor Vitrue, 15 percent of posts should be deleted, because they're offensive or represent promotions unrelated to the brand.
Spammers target big brands' Facebook pages because the exposure is vast, even if the messages remain visible for only a few hours.
This so-called "page spam" can tarnish a brand's image and drive away fans.
Page-spam cleanup is costly because it has to be performed by humans. Some brands are hiring outside firms to do the work, spending as much as $20,000 a month.
