Evan Schuman's StorefrontBacktalk

Amazon has taken a new tack in force-feeding cookies to unwilling customers. A new study from Carnegie Mellon University says Amazon uses a privacy loophole in Internet Explorer to get its cookies onto customers’ PCs, whether they want them or not. Actually, fully a third of the 33,000 sites tested by the CMU researchers used that loophole. But most other sites can at least pretend they’ve done it accidentally. Amazon actually uses its stock symbol, AMZN, to jimmy the system.

Blocked Web cookies are a pain for online retailers. It’s not just inconvenient when you can’t keep track of a customer’s preferences. Many major E-tailers’ checkout systems depend on cookies—including Wal-Mart, Best Buy, Walgreens and Costco—so no cookie means no sale. Fortunately, only a tiny percentage of users completely block cookies, though sites may still run into problems when they try to ditch cookie-blocking customers entirely. But at a time when there are rumblings about toughening privacy laws, it seems like a very bad idea for Amazon to flout users’ privacy preferences—and then sign its name to the violation.

The loophole in question involves a system called the Platform for Privacy Preferences or, as it’s usually identified, P3P. P3P is a way for Web sites to specify their privacy policies to Web browsers using tokens in the form of predefined abbreviations such as DSP and LAW. That way, browsers can automatically compare a site’s privacy policy to users’ privacy settings. IE uses P3P to decide whether to accept cookies.

However, if there’s something wrong with a Web site’s collection of P3P tokens—if a token is misspelled, there aren’t the required minimum of five tokens or some of a site’s tokens contradict others—IE lets the cookies through by default. That’s the loophole. Unlike the subway, in this case, a bad token will get you through the gate.

About 34 percent of the 33,000 Web sites the Carnegie Mellon group examined had bad P3P tokens. Some of those bad tokens appear to be honest mistakes, although the researchers suspect as many as half of the faulty Web sites use the bad tokens intentionally.

But Amazon’s case was clearly not mistyping. It uses just one token: AMZN. That’s nothing like any of the valid tokens. The Internet Movie Database, which Amazon owns, also uses just one token: IMDB.

According to the Carnegie Mellon researchers, “The amazon.com and imdb.com domains each contain a single invalid token and no other tokens, so they fall into the invalid-tokens and missing-tokens categories. It appears that these two Web sites use a CP only for the purpose of avoiding IE cookie filtering.”

Amazon did not respond to a request for comment on what the CMU researchers wrote.

All this may seem like so much under-the-hood minutiae. But in the wake of recent privacy concerns, ranging from Google’s Wi-Fi sampling and iPhone data retention to online chats with pharmacists, customers won’t be more comfortable learning that some online retailers just don’t care about their privacy preferences.