DVB is used in the UK and Europe to send an MPEG-2 stream over the air to television sets. I propose that it be used to send security updates for Microsoft Windows, and if time permits, Mac OS, Debian, Red Hat and other operating systems according to popularity.
Security updates for these platforms
can go into tens or hundreds of megabytes, which is a pain over dial-up internet or if you are charged per byte for usage. DVB can transmit a gigabyte per hour on one channel, so a one hour time slot at 4AM could easily contain all the updates necessary. DVB can have errors in it, but those can be corrected by transmitting some redundant data, perhaps lowering the total transmitted to 500MB, and any blocks still missing could be downloaded at a much lower cost.
Modifying an existing TiVo or Sky+ box to store and make available these updates is only a software problem, and if you have a DVB card in your PC, it's trivial.
There's an existing idea here (linked) about using DVB for generic internet data, but I think this specific application could be a useful starting point. Old hands from the UK might also remember Telesoftware, transmitted over the Teletext system. It's a similar idea to that but that predates the days when computers needed security updates.