In the next few years, a powerful new suite of capabilities will become available to Web developers that could give marketers and advertisers access to many more details about computer users’ online activities. Nearly everyone who uses the Internet will face the privacy risks that come with those capabilities, which are an integral part of the Web language that will soon power the Internet: HTML 5.....

Samy Kamkar, a California programmer best known in some circles for creating a virus called the “Samy Worm,” which took down MySpace.com in 2005, has created a cookie that is not easily deleted, even by experts — something he calls an Evercookie.

Some observers call it a “supercookie” because it stores information in at least 10 places on a computer, far more than usually found. It combines traditional tracking tools with new features that come with the new Web language.
In creating the cookie, Mr. Kamkar has drawn comments from bloggers across the Internet whose descriptions of it range from “extremely persistent” to “horrific.”

Mr. Kamkar, however, said he did not create it to violate anyone’s privacy. He said was curious about how advertisers tracked him on the Internet. After cataloging what he found on his computer, he made the Evercookie to demonstrate just how thoroughly people’s computers could be infiltrated by the latest Internet technology.

“I think it’s O.K. for them to say we want to provide better service,” Mr. Kamkar said of advertisers who placed tracking cookies on his computer. “However, I should also be able to opt out because it is my computer.”