A number of major websites, including Vodafone Group’s website were disrupted yesterday after a Turkish group of hackers broke the Domain Name System (DNS) server that underpins them.The attack appears to have come from the Turkish hacking group TurkGuvenligi, who described the 4th of September as 'World Hackers Day'.Information monitored from the UK said none of Vodafone’s actual websites were directly targeted by the hackers, but the group website was affected.When one types in a website address, the Internet Service Provider (ISP) looks up the underlying Internet Protocol (IP) address of the website via a DNS service.But because the DNS is compromised, it sends back the wrong IP address instead the Vodafone one.Industry analysts say the security breach on the DNS server itself could be fixed swiftly, but it would take up to three days for ISPs to be able to make some people stop seeing the hacked messages.