The Silicon Valley companies that store our personal data have a growing responsibility to protect it from government snooping, according to Daniel Ellsberg, the man who leaked the Pentagon Papers.

Discussing the growing role of Internet companies in the public sphere, Ellsberg said companies such as Google, Facebook, and Twitter need to take a stand and push back on excessive requests for personal data.

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"You're on the spot," he told a roomful of Silicon Valley executives at a Churchill Club event in Santa Clara, Calif., Wednesday night. "You are facing a challenge at this moment of profound implications for our democracy."

Ellsberg was on a panel talking about WikiLeaks and the relationship between the U.S. government -- eager to shut it down -- and corporations such as Amazon, eBay, Visa, and MasterCard -- who all recently severed ties with WikiLeaks in response to government pressure.

Ellsberg's take: If companies don't push back, the government will get too much power as more and more of our private lives -- logged in photo uploads, status updates or online check-ins -- is recorded online.

As the government fights to keep its own secrets, it wants to know as much as possible about our lives, said Ellsberg, who was himself targeted by government investigators after he began leaking classified military documents that described what the U.S. government knew as it escalated its war in Vietnam.

"Facebook, Google, Twitter: Put them all together. If they're all working together, their ability to manipulate us, to know [about us], this is absolutely antithetical to democracy," he said. "People in this audience have the ability to decide that they are ready to take a risk in their lives to fight to preserve democracy in this country and to preserve us from total transparency to our executive branch."

On Thursday, the Electronic Frontier Foundation published 13 electronic guidebooks, from companies such as Facebook and MySpace, used to explain to law enforcement how it should go about requesting sensitive information from those websites. The guidebooks "show that social networking sites have struggled to develop consistent, straightforward policies to govern how and when they will provide private user information to law enforcement agencies," the EFF said.

The issue came up recently when Twitter fought a gag order that prohibited the company from telling users associated with Wikileaks that their Twitter messages had been subpoenaed by the U.S. Department of Justice. The gag orders are typically used to keep criminals from knowing that they are under investigation, but in the case of WikiLeaks, Twitter's lawyers fought the order and won -- allowing the existence of the subpoenas to be made public.

Facebook won't say whether it has had similar requests, but in an email message Facebook spokesman Andrew Noyes shed some light on Facebook's approach. "We are required to regularly push back against over-broad requests for user records. ... [I]n most cases we are able to convince the party issuing legal process to withdraw the overbroad request, but if they do not we fight the matter in court (and have a history of success in those cases)."

Facebook has been hit with a "growing volume of third-party data requests," he said. The company isn't saying exactly how many requests it's received, or how fast the number has been growing, but it's thinking of publishing some data on this in the future.

Google declined to comment for this story.

Earlier in the discussion, Ellsberg talked about the many similarities between his case and that of Bradley Manning, the Army intelligence analyst who is in jail on charges that he leaked classified documents to WikiLeaks. Ellsberg said he felt a "very great affinity with Bradley Manning."

"If Manning were to be tried, he'd have to be tried for treason, and he is no more traitor than I was," Ellsberg said.

Robert McMillan covers computer security and general technology breaking news for The IDG News Service. Follow Robert on Twitter at @bobmcmillan. Robert's email address is robert_mcmillan@idg.com.