First, it's awesome that this rather important subject is getting attention, and kudos to Jen for giving it thought and providing a perspective [1].<p>Logging adds value once an account is compromised, so is a contingency measure (minimising impact). Solving this problem requires mitigation (minimising probability) as well as contingency.<p>Many comments here suggest the use of PKI. PKI is <i>part</i> of a solution and, as with logging and audits, requires more.<p>PKI's biggest problem is that it doesn't scale. The question then becomes one of issuance. Self-issued certificates have no credibility so cannot be trusted. That problem is solved by using a certificate authority that <i>can</i> be trusted.<p>That leads to the next question, which is whom to appoint as a certificate authority (CA)? This thing [2] should scale, so my certificate must work world-wide, with any web site and, while we're at it, offline in meat space.<p>That makes canidates like my bank or a credit check agency bad choices, because they haven't the reach. Credit card companies like Visa, AMEX or Mastercard have better reach, but that only accounts for a tiny percentage of the world's population, because it excludes the poor.<p>The only viable choice then becomes the organisation that <i>already</i> deals in identity - government departments that issue passports, ID cards and driving licences.<p>Of course that's just national. The solution to that problem is to federate identities between governments. Awesome. First part of the problem solved [3].<p>The next part of the problem is anonymity, and it's various variations. This can be solved by using a privacy-enhancing credential - a problem that was solved by Stefan Brands at Credentica [4].<p>The tradgedy is that while these solutions exist, are mature and proven, there is just not enough incentive to make them a reality.<p>Some closing notes: Any good identity system must adhere to <i>all</i> the laws of identity (<a href="http://www.identityblog.com/?p=352/#lawsofiden_topic3" rel="nofollow">http://www.identityblog.com/?p=352/#lawsofiden_topic3</a>). Technologies like OpenId, Persona and OAuth don't even come close. SAML and WS-Federation do a much better job of it, but both SOAP/XML-based. Which makes them unpalatable to many. There's an oppotunity in there somewhere...<p>[1] Logging has been done - just not at the scale Jens envisions. Many military and intelligence systems inform the user of previous acvitivy on login. The better ones use geolocation to tell the user where the most recent logins occured.<p>[2] "This thing" is really an identity meta system.<p>[3] This technology exists in the form of WS-Federation and, to a lesser extent, SAML (which relies on the browser, so doesn't work at the service level).<p>[4] Stefan Brands came up with U-Prove, which was open-sourced by Microsoft after they aquired the technology. IBM have also come up with a privacy-enhancing technology (PET) called idemix (identity mixer). An important attribute of any self-respecting PET is that it <i>must</i> be claims-based, so that it functions in a world of federated identities.