美国联邦调查局说，正在调查联邦调查局、美国司法部和一些娱乐业的网站星期四突然瘫痪的原因。
此前，美国政府关闭了世界上最大的一家文件分享网站。
一个自称为“匿名者”的黑客组织声称发动袭击，这次袭击让有关网站星期四晚间脱机了几个小时。
截至星期五，包括联邦政府网站在内的多数网站已经恢复运行。
星期四早些时候，美国联邦政府关闭了全球最大的文件共享网站之一MU网盘（Megaupload），该网站的创始人和另外六人受到触犯盗版法的指控。
在美国政府的要求下，MU网盘（Megaupload）公司创始人金·道康（金·史密茨）和另外三名高层主管1月19日星期四在新西兰被逮捕。其他三名受到指控的人还没有被缉拿归案。
美国司法部和联邦调查局发表的一份声明说，这是美国政府有史以来“针对版权犯罪行为的最大案例之一”。嫌疑人如果被判有罪，将面临最高为20年的监禁。当局说，MU网盘导致版权所有者损失了超过5亿美元。
MU网盘允许使用者上载和传输容量很大的文件。联邦官员说，这个网站让好莱坞影片等受到版权保护的内容可以免费获得，而且经常是在影片在电影院公映之前。
但是，这家公司以及许多支持它的社会名人说，这个网站主要用于合法文件的传输。
The FBI says it is investigating why the websites for the FBI, the Department of Justice, and several entertainment industry sites all went down Thursday after the government shut down one of the world's largest file-sharing sites.
The hackers' group calling itself "Anonymous" claimed credit for the attacks, which kept the sites offline for several hours late Thursday. By Friday, most had been restored to service, including the federal agencies.
Earlier Thursday, U.S. federal authorities shut down the file-sharing site known as Megaupload and charged its founder and six others with violating piracy laws.
Megaupload founder Kim Dotcom ((aka Kim Schmitz)) was arrested in New Zealand Thursday along with three other top executives at the request of U.S. authorities. Three others facing charges remain at large.
A statement by the U.S. Justice Department and FBI said the action is "among the largest criminal copyright cases" ever brought by the United States. If found guilty, the suspects face up to 20 years in prison. Authorities say Megaupload cost copyright holders more than $500 million.
Megaupload allowed users to upload and transfer very large files. Federal officials say the website used this ability to make copyrighted material, like Hollywood movies, available for free, often before the film was even released in theaters.
But the company, and many celebrity supporters, say the site was mainly used for legitimate file transfers.
