An unprecedented 80,000 hits a minute were recorded from some sites which blocked bookings by genuine passengers, the national carrier's Information Technology (IT) team found during internal investigations.
The IT team identified at least four sites in India, four in the United States and one in Singapore, which were blocking others from getting into the ticket booking engine, airline sources said.
The massive hits led the website's NIC server to turn erratic, they said. Almost all Indian-government websites are developed and managed by the National Informatics Centre (NIC).
In a Facebook post on Wednesday, the national carrier had apologised to its "customers who tried to access our website during the last few hours. We are experiencing some technical problem with our servers and doing everything to minimise the amount of time necessary to restore our website."
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Air India had on Tuesday announced discounted tickets offer for Rs 100 for a limited period to celebrate its merger with erstwhile Indian Airlines. The bookings can be done till August 31 for travel till September 30 only through the airline's website.
An official release said the airline was also "exploring" to take up the issue at an appropriate forum.