A worker calls up a sensitive investor list and downloads it on her thumb drive, slips it into her pocket, and walks out, smiling and waving to her boss and the security officer stationed at the front door. According to one recent study, IT managers said portable storage devices, such as thumb drives and MP3 players, have surpassed even malware to become a top concern. The study, which polled 370 IT professionals, showed that 38.4% of IT managers say portable storage devices are their top security concern.