If you are using Debian at work and you need to update/upgrade or even install any debian package through apt and you are behind some MS proxy server (that's my case) you need to install ntlmaps package and export some variables:
echo -n username:
read -e username
echo -n password:
read -es password
echo -e \nProxy environment variable set.
Don't forget to change: proxyaddress:port. With this everything should work.