Unlike Apple, Google welcomes the Tech community to modify and tweak devices to their own needs.  Here is a Youtube video by GTV Hacker who hacked the Chromecast bootloader, and found out that it is using a modified version of  the Google TV software. For the exact details on how GTV Hacker managed to hack and root the Google Chromecast, visit his blog here, http://blog.gtvhacker.com/2013/chromecast-exploiting-the-newest-device-by-google/