The rub comes when a user is asking for a nonexistent subdomain of a real website, such as
http://webmale.google.com, where the subdomain webmale doesn't exist (unlike, say, mail in mail.google.com). In this case, the Earthlink/Barefruit ads appear in the browser, while the title bar suggests that it's the official Google site.
As a result, all those subdomains are only as secure as Barefruit's servers, which turned out to be not very secure at all. Barefruit neglected basic web programming techniques, making its servers vulnerable to a malicious Javascript attack. That meant hackers could have crafted special links to unused subdomains of legitimate websites that, when visited, would serve any content the attacker wanted.
