Comment 10 for bug 1243090

I can reproduce this issue here if I install ttf-mscorefonts-installer and then "simulate" a network failure via disconnecting my network cable after the download started. If its already installed you can also run from the checkout:
$ cd data ; sudo rm /var/lib/update-notifier/package-data-downloads/ttf-mscorefonts-installer ; sudo ./package-data-downloader

With the default version this hangs until I press ctrl-c for me. With the version from https://code.launchpad.net/~mvo/update-notifier/socket-timeout it will fail after the timeout is reached.