Obviously, most of the deceitful scum doing this are porn websites, and frankly, I have little sympathy. But one of them is TheSun.co.uk, the online version of Rupert Murdoch's grubby little comic.
Quite shockingly, some respectable companies are up to it too:
YouPorn tops the list, but PerezHilton, Technorati, TheSun.co.uk, and Wired are also spying on their users' browsing habits by exploiting this vulnerability.
Stay away from those sites, or switch on 'private browsing' on Firefox and possibly Safari.