Philipp Lenssen —”This looks like a bit of a privacy hole in browsers. Using JavaScript which reads out link style attributes, a page can determine which URLs in a given URL list have been visited.”

For example, in the CSS you can define visited links to have larger padding than non-visited links, and now you can iterate through the list of links and check against the “offsetHeight" value... if it’s the higher value, the URL was visited.

Naturally, this information can now be transmitted to the server using AJAX or a form submit. I wrote a very small test case (works in IE and FF) based on findings by Scott Schiller.

Micro Persuasion | Google Blogoscoped

Trace What URLs You Have Visited