— -- The hacker group Lizard Squad has claimed responsibility for attacking Malaysia Airlines' website on Sunday. Users who logged onto the Malaysia Airlines website were greeted with the image of a lizard in a top hat and the message: "404 -- plane not found."
Below that were the words: "Hacked by Lizard Squad -- official Cyber Caliphate."
The attack came after a difficult year in which the airline lost two flights, including one that has yet to be found.
At issue in the hack attack is whether Lizard Squad obtained any private information belonging to passengers. The group tweeted late Sunday that it planned to dump data found on the airline's servers. Malaysia Airlines said in a statement that "user data remains secured."
The company acknowledged its website was having issues late Sunday. The website was fully operational again mid-afternoon Monday in Malaysia.
"Malaysia Airlines confirms that its Domain Name System (DNS) has been compromised where users are re-directed to a hacker website when www.malaysiaairlines.com URL is keyed in," a statement today from the airline said. "At this stage, Malaysia Airlines' web servers are intact. The airline has resolved the issue with its service provider and the system is expected to be fully recovered within 22 hours."
"Making claims of data theft is serious and should be taken seriously," Robert Siciliano, an online safety expert to Intel Security, told ABC News. "Those who have information stored on the site, such as personal information and credit card numbers should take heed and take steps to ensure their accounts are secure. Monitor statements looking for unauthorized activity. Beware of phishy emails and avoid clicking links. Otherwise pay attention to news reports and look for the airline to send out a communication."
Malaysia Airlines said it has also reported the incident to CyberSecurity Malaysia and the country's Ministry of Transport.
Lizard Squad has previously claimed responsibility through tweets for attacking the Sony PlayStation and Xbox networks over Christmas, and earlier this month, the "Cyber Caliphate" briefly took over the Twitter and YouTube accounts of U.S. Central Command, authorities said.
Known for its trollish and prankster style, Lizard Squad's weapon of choice is most commonly the DDoS (distributed denial of service attacks), which flood a target's servers with fake traffic, knocking it offline.
While authorities have Lizard Squad on their radar, making arrests has proven to be difficult as the tech savvy group is dispersed around the world.
After a joint investigation between the FBI and authorities in the United Kingdom, an 18-year-old man was arrested earlier this month in northwest England as part of an investigation into the Christmas gaming attacks.