In order to ensure that the iTunes store stays in business, Apple uses digital rights management protection, limiting the number of authorized computers that can play content from an Apple account to five. In other words, if you download content from iTunes onto your iPod and then plug your device into an unauthorized computer, you won’t be able to enjoy that content. The only exception is music files, which come without protection and can be played on any computer. To enjoy other types of content though, like video and audiobooks, you must authorize computers.Read More »How to Authorize Computer on iPhone