3. Internet Explorer 6
Beginning in the mid-1990s, Microsoft fought the browser wars against Netscape with all it had. With Internet Explorer 6, released in 2001, though, it seemed to declare "Mission accomplished." For five long years, IE barely changed, even as competitors such as Firefox and Opera showed there were plenty of ways to make browsing better. At the same time, attacking IE 6 security holes became a full-time occupation for an army of hackers--and patching them up turned into part-time work for everyone who used the browser. IE 7, released in 2006, is a passable upgrade, but wouldn't the world have been a better place if it had shown up two or three years earlier?