The DNS settings of a number of major Web sites were hacked on Monday and many visitors were redirected to a Turkish hacker's Web site.
The hacked Web sites include The Daily Telegraph, UPS, Vodafone, National Geographic, The Register and many others. All the hacked Web sites are currently experiencing disruption, according Zone-H, a site that monitors website defacements.
The hackers told The Guardian in an email interview that they were experts in exploiting web vulnerabilities and did so for entertainment.
On being asked if this was planned for a long time and executed, they replied: "We usually choose some big targets and find a way to access them. Sometimes, it takes months. But harder makes it funnier. [It was] not by chance because we are expert of all kinds of web vulnerability holes."
They said they had targeted the sites for long and found that the DNS records of the sites were the easiest way to achieve their ends.
The hackers added: "The hardest one is reaching the domain company. But if you can succeed, there will be a treasure for you."
Although the sites were not hacked directly, the attack has put users at risk of having passwords and other details stolen. If the users attempt to log into the fake third-party sites under the hackers' control, their account would automatically be hacked.
The hacking group had later tweeted: "Millions of dollars, large systems, small weaknesses and what I could do. Just for fun."