A group identifying themselves as "anti-fascist hackers" broke into the website and e-mail account of controversial British historian and accused Holocaust-denier David Irving and obtained his private communications as well as attendee lists for his current U.S. speaking tour.

The hackers posted Irving's e-mail correspondence online, as well as the user name and password for his website account and AOL e-mail account, which shared the same password. The hackers also posted the e-mail addresses and other personal information – such as names, phone numbers and shipping and credit card billing addresses – of people who made donations through his websites, purchased his books or bought tickets for his appearances.

Irving's username and password for his Authorize.net account, which handles the credit card transactions on his website, were also exposed.

The data was posted on whistle-blowing site WikiLeaks on Friday evening in advance of Irving's Saturday speaking engagement at the Catholic Kolping Society of America in New York City. The organization reportedly canceled the event on Friday after someone contacted it.

The organization said its facility had been booked a few days ago by someone using the name "Michael Singer," who said he wanted to hold a book reading. The organization canceled the engagement after learning that the event was scheduled for Irving.

The location of Irving's engagements are generally kept secret and announced to attendees only at the last minute to prevent protesters from appearing at the venues or pressuring facilities to cancel Irving's reservations.

Irving was once a popular historian specializing in World War II but has been a lightning rod for controversy over opinions he's expressed in the past about the Holocaust and the Nazi regime. Although he asserts he's not a Holocaust denier, he was convicted in Austria in 2006 of denying the Holocaust and sentenced to three years in prison, and was called a racist and anti-Semite by a British judge in a libel case that Irving lost. He has underplayed the extent of the extermination of Jews, saying the number killed was much fewer than 6 million. He also claimed in 1989 that Auschwitz was not an extermination camp – though he has since recanted.

"History is a constantly growing tree – the more you know, the more documents become available, the more you learn, and I have learned a lot since 1989," the BBC reported him saying.

The Anti-Defamation League considers him one of the world's most effective purveyors of Holocaust denial and has carefully monitored his activities.

The e-mails published on Friday exposed discussions that occurred between Irving and others about booking his speaking engagements under pseudonyms to thwart protesters.

"The venue is reserved under my name . . . , my phone number and wonderfully disguised . . . as a book signing, not yours or some group so just in case some nasty is poking around they will come up with nothing," wrote one supporter in the U.S. who had booked an engagement for Irving in Richmond, Virginia.

The e-mails include other personal correspondence about the East Coast speaking tour Irving is currently conducting in the U.S., security issues – such as an incident involving weapons that someone brought to one of his recent speaking engagements in Florida – and a tense exchange between Irving and his assistant about his poor treatment of her and her threats to quit.

The data also includes the bank account number of Irving's landlord in the United Kingdom and instructions to Irving's bank in Florida to wire money to the account, as well as personal exchanges with supporters.

One supporter writes to Irving: "You should continually blame the Jews who controlled Churchill with causing their own disaster. Also blame the Jews for the loss of your empire and the immigration invasion caused by it. As Reichminister Goebbles, of Blessed Memory, loved to say, 'The Jews are to blame.'"

Among the published data is a list of people who bought tickets for Irving's speaking engagements through his website. The word "Achtung" has been appended to some ticket orders that appear to come from Jewish attendees. The published e-mails discuss playing tricks on attendees believed to be Jewish, such as giving them a false address for speaking events.

Irving's website was inaccessible Friday evening and calls to cell phones belonging to Irving and his assistant went unanswered. But Michael Santomauro, whose correspondence with Irving was among those posted online, confirmed that the e-mails were authentic and that Irving had been hacked.

Santomauro identified himself as the "Michael Singer" who had booked Irving's New York speaking engagement. He told Threat Level that around 7p.m. Friday evening an e-mail was sent out by the hackers from Irving's AOL account shortly before Irving was scheduled to give a talk in New Jersey. The e-mail was sent to a list of Irving supporters with the subject line reading: "ADVISORY: Anti-Fascist Hackers Destroy Holocaust Denier David Irving's Website and Release Private Emails, Attendee Lists."

The e-mail contained all of the information that was posted on the WikiLeaks website and indicated that the hackers destroyed all the files, including backup files and databases, on Irving's web sites irvingbooks.com and fpp.co.uk.

In the e-mail, the hackers wrote: "We did this to expose this Nazi-sympathizer for who he is and to shut down/disrupt any possibility of Irving rearing his fascist head in public during his tour. To David Irving and all aspiring white-power, anti-immigrant, queer-bashing, racist pigs – give it up! We will fight you on the streets and on the internet until you are swept into the dustbin of history."

Santomauro said there was an inkling that something was wrong about half an hour before the hacker's e-mail arrived when Irving contacted him to tell him the New York event had been canceled and asked how his detractors could have learned the location. The two had only discussed it among themselves by e-mail and by phone.

"Apparently [the hackers] have been monitoring his AOL for a certain amount of time," Santomauro said.

He told Threat Level he suspected the Jewish Defense Organization was behind the hack. He says he's been targeted himself by protesters from this group and others who have harassed him outside his apartment building and hacked the account for a Yahoo study group he runs.

But, he says, the harassment against Irving is much worse.

"I don't agree with everything Irving has to say, but he should have the freedom to express whatever views he has," Santomauro said. "I can agree that he's not a very pleasant person. But he's not a Holocaust denier. He could care less about it and is not very knowledgeable about it. . . . He doesn't talk about it in his speaking tours."

The Jewish Defense Organization denied responsibility for the hack.

"We applaud the act, but we have no idea who did it," said spokesman Jeff Klein. "This is the first we've heard of it."

UPDATE: Irving's assistant, Jaenelle Antas, forwarded a statement from Irving saying that it would be several days before he could assess the damage from the hack, since his web provider had apparently scheduled repairs to begin on Friday – the day of the hack – and last for seven days, making it difficult for him to access his account.

"We have a complete back-up, in any case," he wrote. "Half the files [the hackers] posted were already publicly available on the website, like the Radical's Diary. Other items they appear to have invented. We shall be apologising to the many people who may find themselves inconvenienced by these juvenile cyber-nasties. We are puzzled that they are so frightened by historical debate."

Antas did not respond to a follow-up question asking which items the hackers posted were invented.

This post was updated with a response from the Jewish Defense Organization.