Joe Cadillic sends along this information from Public Intelligence, who compiled a 5-page list of Twitter accounts followed by the Dept. of Homeland Security National Operations Center (@DHSNOCMMC1). They note that “in accordance with DHS Privacy direction, DHS NOC MMC follows only authorized accounts and never follows accounts of private individuals.”
You can download the list here (pdf), which was the list as of July 11. As of today, that account follows 340, but their tweets are protected and you cannot see which accounts they are following by clicking on the “Following” link.