I've just installed Debian 6.0.4 on VirtualBox, and I'm trying to install g++. So, into the terminal I typed:
aptitude install build-essential
But it's trying to get the package from disk:
Media Change: Please insert the disc labeled 'Debian GNU/Linux 6.0.4 _Squeeze_ - Official i386 CD Binary-1 20120128-12:53' in the drive '/media/cdrom/' and press [Enter].
Why isn't it just downloading it from Debian's repositories? Can I change this behavior?