FYI…

- http://zdnet.com.com/2102-1105_2-5313402.html?tag=printthis
"…According to the researchers, an unpatched Windows PC connected to the Internet will last for only about 20 minutes before it's compromised by malware, on average. That figure is down from around 40 minutes, the group's estimate in 2003. The Internet Storm Center, which is part of the SANS Institute, calculated the 20-minute "survival time" by listening on vacant Internet Protocol addresses and timing the frequency of reports received there…"

- http://isc.sans.org/
Survival Time - Average time between attacks: 18 minutes
(as of date/time of this post)

Surival Time History
>>> http://isc.sans.org/survivalhistory.php
"The survivaltime is calculated as the average time between reports for an average target IP address. If you are assuming that most of these reports are generated by worms that attempt to propagate, an unpatched system would be infected by such a probe. The average time between probes will vary widely from network to network…University Networks and users of high speed internet services are frequently targeted with additional scans from malware like bots. If you are connected to such a network, your 'survival time' will be much smaller. The main issue here…the time to download critical patches will exceed this survival time…"

Windows XP: Surviving the First Day
>>> http://www.sans.org/rr/papers/index.php?id=1298

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