By Joseph Menn SAN FRANCISCO, Jan 17 (Reuters) - Several prominent computer security experts have canceled appearances at the largest annual U.S conference on security technology and are instead switching to a rival gathering, as discord grows over U.S. intelligence practices. Nine security experts have ditched coveted speaking slots at the annual RSA Conference, to be held next month in San Francisco, in protest over the conference owner's dealings with the National Security Agency. Instead, they will speak at the new and smaller 'TrustyCon' gathering to be held in the same city during the RSA event, billed as the first 'Trustworthy Technology Conference.' Backers include Def Con, which holds a major hacking conference each year in Las Vegas and the nonprofit Electronic Frontier Foundation. Reuters reported last month that RSA Security, now a division of data storage maker EMC Corp, incorporated a flawed cryptography formula in a widely-used software tool under a $10-mil federal contract. The NSA-developed formula is now believed to have been breakable by the agency, though people familiar with the RSA arrangement told Reuters that executives had not realized that at the time. "I don't think it's wrong for companies to work with the government. What's important is being trustworthy and honest with customers," said Alex Stamos. Stamos is involved in the setting up of TrustyCon. "The most charitable reading is that RSA failed to see the danger and didn't warn the customers." RSA continued to use the NSA formula for years despite cryptography experts calling it suspicious, recommending its removal only when reports based on NSA documents leaked by former U.S. spy agency contractor, Edward Snowden prompted a federal standards body to drop its endorsement of the technology. RSA said in December that it never knowingly compromised products and that a decade ago the NSA had been seen as a helpful partner in developing security tools. But Def Con founder, Jeff Moss said RSA "seemed to lack a genuine interest in engaging with its customers" about what it had done and why, as well as what it had learned. The RSA's executive chairman, Art Coviello, is scheduled to give one of the keynote speeches at the RSA event. "It is not unusual for small events to happen alongside that aim to leverage the momentum and publicity of the RSA Conference, which is a good sign of a thriving industry event," the conference's organizers said in a statement on Friday, referring to the rival gathering. "We've always embraced these activities and the open, healthy dialogue that springs from them." DISAPPOINTMENT Owned by RSA parent EMC, the RSA Conference depends on outside advisors to select topics. The program committee chair this year is Hugh Thompson, chief security strategist at Blue Coat Systems Inc. In an interview, Thompson said that while he was disappointed that some speakers had canceled, there would still be a great deal of discussion about Snowden's revelations and the roles played by RSA and its peers. "There are a lot of questions that have been raised about the security infrastructure and how it works, and I do think it's going to lead to a very healthy debate," Thompson said. "This is a topic that is definitely going to be discussed." More than 500 speakers will speak at the RSA Conference, which organizers expect to attract more than last year's record 24,000 attendees. Among those withdrawing from the RSA Conference include Mikko Hypponen, chief research officer at Finland-based security company F-Secure, two researchers from Google Inc , and Jeffrey Carr, a consultant who runs his own conferences on cyber intelligence-gathering and defense. Some said the RSA deal struck such a nerve because it is the first security company to be identified as having a contractual relationship with the NSA that ultimately weakened security. Others have slammed the conference withdrawals, citing many companies and different countries are guilty of similar, unreported behavior. Hypponen, Moss, and RSA critics from the Electronic Frontier Foundation and American Civil Liberties Union will be among the TrustyCon presenters, Stamos said. Hypponen's speech will cover malicious software created by governments.