caribguy - 3:57 pm on Aug 12, 2011 (gmt 0)
UA stands for user-agent, i.e. the browser. Your browser also gives out a few dozen other nuggets, like screen size, installed flash version, plugins, browsing history, etc... That can also help to uniquely identify your machine.
If you want to take it one step further, you could add persistent flash cookies to the mix.