Baidu filed the suit in New York on against Register.com, claiming the domain registrar's "gross negligence" lead to the search giant being "unlawfully and maliciously altered", the company said in a statement on Tuesday.
Baidu's site was disabled for several hours January 12, and visitors were re-directed to a site where a group calling itself the Iranian Cyber Army claimed responsibility for the attack. The same group had taken credit for a similar attack on Twitter in December.
Baidu said its Chinese site — Baidu.com.cn — was unaffected by the outage. Baidu controls about 62.2 percent of the Chinese search market compared with Google's 14.1 percent, according to ComScore numbers for November 2009.
For more on this story, read "Baidu.com sues US domain registrar over hacking" on CNET News.