The Provo, Utah-based company said Ancestry.com and its sister site, Findagrave.com, were targeted on Monday in the attack that flooded servers with traffic and caused them to crash.
In a post on Ancestry's Facebook page on Wednesday, the company said some features had been disabled as a precaution and asked users for patience while the service was completely restored.
No consumer data or information was compromised during the attack, Scott Sorensen, the company's chief technology officer, said in a separate statement. The company's staff are working to prevent future hacking incidents, he added.
"We want to apologize for the inconvenience this has caused and also thank you for your amazing support, as this may have interrupted some of your family history research," Sorensen told users. "We appreciate your patience."
Originally founded as a publishing company in 1983, Ancestry.com bills itself as the world's largest online family history resource, with more than 2 million subscribers.
The company says its databases hold more than 14 billion records, that it is adding some 2 million more every day, and that its customers have used its services to draw up more than 60 million family trees.
© Thomson Reuters 2014
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