charles@charles-VirtualBox:~$ sudo apt-get update
Get:1 http://extras.ubuntu.com trusty InRelease [8,127 B]
100% [1 InRelease gpgv 8,127 B] [Connecting to us.archive.ubuntu.com (91.189.91Splitting up /var/lib/apt/lists/partial/extras.uIgn http://extras.ubuntu.com trusty InRelease                                  
E: GPG error: http://extras.ubuntu.com trusty InRelease: Clearsigned file isn't valid, got 'NODATA' (does the network require authentication?)
charles@charles-VirtualBox:~$