CSS の visited を利用してブラウザの訪問履歴を取得されうるユーザは 76 % 以上に上る
対策
Firefox 3.5 users will be happy to learn that their browser has a configuration option which disables visited links. To enable it, type in about:config in the address bar and set the layout.css.visited_links_enabled option to False.
For browsers which allow custom user stylesheets to override page defaults, you can use the following stylesheet to disable resource downloads for visited links. This only helps if you have scripting disabled by browser configuration or through an extension such as NoScript. Since we can't test this code it in all possible browsers, make sure that it has the desired effect for your setup:
:link, :visited, :link *, :visited * {
background-image: none !important;
list-style-image: none !important;
border-image: none !important;
border-corner-image: none !important;
-moz-border-image: none !important;
-webkit-border-image: none !important;
}
