Every time browser developers and others come up with a defense against tracking -- the use of tiny bits of computer code that tells Web sites where you've been on the Internet -- the other side ups the ante with a new trick. And it's happening again.

A researcher at Stanford University recently found that Microsoft has been using an online tracking technology that allowed the company to sneakily track users on MSN.com even though it had used some of the standard techniques developed to avoid tracking.

Another group of researchers found that other sites, including Hulu.com, employed super cookie techniques to track users for advertising purposes. : "We found two sites that were respawning cookies, including one site -- Hulu.com -- where both flash and cache cookies were employed to make identifiers more persistent. The cache cookie method used Etags, and is capable of unique tracking even where all cookies are blocked by the user and 'private browsing mode' is enabled." (The authors are from The University of California at Berkeley, Worcester Polytechnic and the University of Wyoming. The emphasis is mine.)

Shortly after surfaced last week, Microsoft announced that it would stop the use of the so-called super cookies on MSN. A few days after the UC Berkeley report was published, Hulu : "Upon reading the research report, we acted immediately to investigate and address the issues identified. This included suspending our use of the services of the outside vendor mentioned in the study."

Hulu says that the super cookie technology was used by two of their outside vendors, an attempt, the report notes, by Hulu to absolve itself of responsibility. You can decide for yourself if you buy that. But more to the point, what can you do to defend yourself?