Shanghai-based Ctrip.com said it was put out of service yesterday as a result of an "unknown hacker attack."
"Part of the company's servers were attacked at 11:09 a.m., which led to the temporary collapse of its website and mobile application," a press officer told Shanghai Daily.
Engineers fixed most of the problems on 10:45 p.m. last night, though some functions remain out of service. Visitors were advised to visit eLong.com, a subsidiary of Ctrip.
However, that site too was out of service for about an hour.
A statement by eLong about 6 p.m. said it had been attacked.
The problem was fixed and operations resumed about 7 p.m..
Ctrip claimed that the attack had not resulted in the loss of any of its customers' personal data or booking information.
"The 'business codes' were deleted and I suspect an insider did it out of revenge," an Internet user said on weibo.com.
Li Tiejun, who works for Beijing-based Internet security firm Cheetah Mobile, said the problem was likely caused by an internal management problem, "because hackers usually target data and don't try to interrupt systems."
Ctrip's problems came after services were suspended on Wednesday at Alipay, China's biggest third-party payment tool.
Several customers could not use Alipay for about two hours after an underground fiber optic cable was damaged by construction workers in Hangzhou.
"Chinese Internet companies must pay attention to safety issues as giants like Alipay and Ctrip appear to be vulnerable to attack," said Tan Xiaosheng, deputy president of Qihoo 360, China's biggest online security firm.
