The airline said in a statement on its Facebook page that its Domain Name System (DNS) was compromised and as a result users trying to access the URL www.malaysiaairlines.com were being redirected to a hacker website.
At this stage, Malaysia Airlines' Web servers are intact, it added. The airlines assured customers that it had not been hacked and "this temporary glitch does not affect their bookings and that user data remains secured."
The Lizard Squad countered the claim of the airlines and released what appeared to be a travel itinerary receipt as proof that it had hacked into user data.
Users were initially redirected to a page with a picture of a Malaysia Airlines plane with the message "404-Plane Not Found. Hacked by Cyber Caliphate," a reference to the disappearance of the airline's Flight MH370 when on a flight in March between Kuala Lumpur and Beijing. The page was subsequently modified to have the logo of the Lizard Squad. At the bottom of the image was another message "Hacked by LIZARD SQUAD -OFFICIAL CYBER CALIPHATE."
Malaysia Airlines said it had resolved the issue with its service provider and the system is expected to be fully recovered within 22 hours. "The matter has also been immediately reported to CyberSecurity Malaysia and the Ministry of Transport." It was directing passengers who wanted to book fares to a page on its site.
Lizard Squad claimed in December it was behind distributed denial-of-service attacks on Christmas Day of Sony's PlayStation Network and Microsoft's Xbox Live.
But it appeared to share credit with other groups for the attack on Malaysia Airlines, including the Cyber Caliphate, according to screenshots of the website.
After another attack on Sony in August, the Lizard Squad had said in a Twitter message that "today we planted the ISIS flag on @Sony's servers," referring to the militant group that occupies parts of Iraq and Syria. On Monday, visitors to the Malaysia Airlines website said that at one point they noticed a browser tab "ISIS will prevail." A group, calling itself CyberCaliphate, compromised the Twitter account of the U.S. Central Command (CENTCOM) earlier this month.