A website has published what it says are 573,000 intercepted pager messages sent during the 9/11 attacks in the United States.
Wikileaks says it will not reveal who gave it the messages - some of which are from federal agencies as well as ordinary citizens.
Internet analysts say they believe the messages are genuine but federal authorities have refused to comment.
The attacks on 11 September 2001 left nearly 3,000 people dead.
The messages are being published over a 24-hour period, ending at 0800GMT on Thursday. They are being released simultaneously on Wikileaks and social networking site Twitter.
The website is broadcasting each message at the time it was sent originally in 2001.
The first message was from 0300 local time (0800 GMT), five hours before the first attack in New York and the last 24 hours later.
The messages are not all about the attacks. Some are mundane questions about what people are having for lunch.
However, many are about the deadly plane attacks and range from people trying to find out if their loved ones are safe, to government messages, to computer server errors.
They include messages such as
New York's fire and police departments said they could not comment on whether messages purportedly sent from them were genuine while the US Secret Service refused to comment.
Pager company USA Mobility said it was troubled by the alleged interceptions, the Associated Press news agency reported.
Wikileaks allows people to anonymously post documents on the web, saying its aim is to promote transparency.
It was created in 2006 by dissidents, journalists, mathematicians and technologists from the US, Taiwan, Europe, Australia and South Africa.
Wikileaks spokesman Daniel Schmitt said the messages were submitted anonymously to the site several weeks ago.
He told Associated Press: "From the context information that the source provided we have strong reasons to believe that this is valid data."
He said the messages would help provide a fuller picture of what happened that day.