I have noticed in my Visitors log that some users are being counted as multiple unique users. Their IP addresses seem to change each time, but tracking each user by IP address alone is not an efficient method of tracking for this very reason. Piwik needs to be able to track a user across the site even if their IP address shifts.
Keywords: ip address, cookies, sessions, duplicates, multiple
We fixed a related issue in 1.7 beta please update (it has no known bug) http://forum.piwik.org/read.php?2,83913
If after updating, for new visits, you still get the problem, then please comment here again