Data routinely gathered in Web logs - IP address, cookie ID, operating system, browser type, user-agent strings - can threaten online privacy because they can be used to identify the activity of individual machines, Microsoft researchers say.



From PCWorld:

The researchers found that 62% of the time, HTTP user-agent information alone can accurately tag a host. Combine that same information with the IP address, and the accuracy jumps to 80.6%. If the user-agent information is combined with just the IP prefix the accuracy is still 79.3%, they say.

The highest accuracy came when more than one user ID was linked to a single host, as would be the case in a family that shares a single computer. In such cases, multiple IDs would accurately represent that one host computer. The accuracy rate was 92.8%.

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