Hoople - 1:32 am on Dec 7, 2010 (gmt 0)

"...The technique the University of California, San Diego researchers investigated is called “‘history sniffing" and is a result of the way browsers interact with Web sites and record where they’ve been. A few lines of programming code are all a site needs to do that..." [bostonherald.com ]

The article goes on to mention that recent versions of Safari and Google Chrome have this security loophole fixed.