A number of major websites -- including Vodafone's Group website -- were disrupted yesterday after an apparently Turkish group of hackers were able to break the DNS server that underpins them.

When you type in a website address, your ISP looks up the underlying IP address of the website via a DNS service. If that is compromised, then it might send back the wrong IP address -- which is what appears to have happened in this case.

None of the company's actual websites were directly targeted by the hackers.

The attack appears to have come from the Turkish hacking group TurkGuvenligi, who described the 4th of September as 'World Hackers Day'.

Although fixing the security breach itself can be a swift affair for the DNS server, as ISPs around the world cache the results to save looking them up for every request, it could take as much as three days for some people to stop seeing the hacked messages.
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Hacked DNS message