The DuPage Medical Group is notifying patients about a data security breach. DMG experienced an issue last month that caused a disruption to its network systems. Through an investigation, it was determined that the network outage was caused by unauthorized people who gained access to the DMG network. Officials found out later that certain files that contained patient information may have been impacted by the this incident. DMG is in the process of mailing letters to people whose information may have been involved.