Javascript Can Examine The Color Of Your Links = Steal Your Browsing History

Javascript can examine the rendered state of an HTML document, called the DOM. One of the properties that is available through the DOM is the current CSS attributes of a node (nodes are HTML tags, one of which is the or link tag).
All a website has to do to see what pages you’ve been to is place a list of links on the page and examine the color of those links. Ajax can be used to retrieve a list of links to test and also send the results back to the server without the user ever knowing.
The code to do this examination can be a little tricky due to cross browser issues. Here is a snippet of Javascript that can do the evaluation

function hasLinkBeenVisited(url) {
var link = document.createElement('a');
link.href = url;
document.body.appendChild(link);
if (link.currentStyle) {
var color = link.currentStyle.color;
if (color == '#ff0000')
return true;
return false;
} else {
link.setAttribute("href",url);
var computed_style = document.defaultView.getComputedStyle( link, null );
if (computed_style) {
if (computed_style.color == 'rgb(255, 0, 0)')
return true;
}
return false;
}
}

The code above assumes that CSS rules are making links that have been visited red (#ff0000) and new links a different color.