It’s too bad he’s evil. This hack is marvelous!
Explanation of the hack for the non-technical:
Have you ever noticed that after you visit a link, your web-browser displays it as a different colour? (The default colors are blue for unvisited and purple for visited.)
Well, the hack is to write a web page that programatically inserts a bunch of links, and then looks at the colours of the links to see if they’ve been visited.
Because the web-browser automatically sets the link colours for you according to your browser history, this hack essentially gives the webpage access to your browser history. Well, not quite. It can check a predefined list of sites against your browser history to see if you’ve been there.
Brilliant.