At the end of the (under)wire is ... a person
During the work of writing the W3C's P3P spec we considered whether an ipv4 address, an end-point identifier, was personally identifying information. We agreed that a complete ipv4 address -- a dotted quad -- numbers of the form 36.26.36.dd (to pun on Avedon Carol's Bra-of-the-Week standard) was "PII", but disagreed as to how much of the dotted-quad to delete so that the remainder would no longer be personally identifying information.
TheP3P Spec Working Group adopted Martin Presler-Marshall's (IBM) definition -- "a partialip element represents an IP version 4 address (only - not a version 6 address) which has had at least the last 7 bits of information removed."
My position was that 7 bits was insufficient, and we needed to limit the bits collected to 16 out of the 32, to avoid off-line and on-line data collection correlation from transforming a partialip element into a unique personal identifier. I won't argue with people who think that because they are behind a commercial or residential NAT or in a (not very dynamic over time, and wicked static for days and weeks on end) ISP managed DHCP block, they are "anonymous". They're wrong. But the Working Group went with the 7bit mask.
Today Peter Scharr issued a ruling for the member states of the European Union, that ip addresses are personal data. Google/DoubleClick differs of course, which is amusing when you consider that DoubleClick's core business model was, and is, deterministic, not statistical, behavioral profiling. Its the difference between knowing that 36.26.36.dd statistically appears to be a person-with-breasts, and knowing that the person is named Jane Doe, and having access to her credit-card transaction history, including her shopping at Bras of the World, and every other bit of linked data Equifax et alia sell.
For background see European Commission > Justice and Home affairs > ... > Data Protection page.
Of course, none of this applies in the US, where everyone is wiretapped. Don't forget you could have supported Chris Dodd in Iowa, and you can still support Chris Dodd on the coming FISA replay.
