According to the SANS Institute's Internet Storm Center Survival Time data there is only an average of 17 minutes between network probes or attacks on the Internet. Theoretically, if you take a brand new Windows XP computer out of the box and plug it in to the Internet you have less than 20 minutes to download and apply the appropriate patches and updates before your computer is compromised or infected in some way.

Obviously it isn't possible to download the patches in that time- even over a broadband connection. Users would have to be supplied with CD's packed with all necessary updates and instructed not to connect to the Internet until they are all applied.

Scott Granneman discusses the Survival Time data and its implications for home users and network security in this Security Focus article: Infected In 20 Minutes