Washington - A new letter from intelligence investigators to the Justice Department says secret government information may have been compromised in Hillary Clinton's private server, underscoring an inescapable reality for her presidential campaign: E-mail is forever.Clinton, the former secretary of state and now the leading Democratic presidential candidate, wants to focus on the economic issues she and her team believe will drive the next election. But they remain unable to fully escape the questions surrounding her decision to run her State Department correspondence through an unsecured system set up at her New York home.The inspector general of the US intelligence community recently alerted the Justice Department to the potential compromise of classified information arising from Clinton's server. The IG also sent a memo to members of Congress indicating that "potentially hundreds of classified e-mails" were among the 30 000 that Clinton had provided to the State Department - a concern the office said it raised with FBI counterintelligence officials.The memo also made recommendations for changes in how the e-mails are being reviewed and processed for public release.Though the referral to the Justice Department does not seek a criminal probe and does not specifically target Clinton, the latest steps by government investigators will further fuel the partisan furor surrounding the 55 000 pages of e-mails the State Department already has under review.A statement from the intelligence inspector general, I Charles McCullough, and his counterpart at the State Department, Steve Linick, said that McCullough's office found four e-mails containing classified information in a limited sample of 40 e-mails."This classified information should have never been transmitted via an unclassified personal system," they said.For Clinton, the news amounted to a major distraction on a day she'd hoped to focus on unveiling a new set of economic policies. Instead, she opened her New York City speech by addressing the controversy, decrying some reports as inaccurate.Criminal investgationSome media initially reported that the Justice Department had been asked to consider a criminal investigation into whether she mishandled her e-mails."We are all accountable to the American people to get the facts right, and I will do my part. But I'm also going to stay focused on the issues," she said.It was not immediately clear whether the Justice Department would investigate the potential compromise the intelligence inspector general highlighted. The office has not suggested any wrongdoing by Clinton, according to US officials speaking on the condition of anonymity because they were not authorised to discuss the referral publicly.But the inspector general's office said in its letter to congressional oversight committees that it was concerned that "these e-mails exist on at least one private server and thumb drive with classified information and those are not in the government's possession," said Andrea Williams, a spokesperson for McCullough.None of the e-mails was marked "classified" at the time they were sent or received, but some should have been handled as such and sent on a secure computer network, the letter sent to congressional oversight committees said.Clinton has maintained that she never sent classified information on her personal e-mail account, which she said in March she used as a matter of convenience to limit her number of electronic devices.The State Department has made public some of the e-mails involving Clinton, and is under court order to make regular further releases of such correspondence.The aim is for the department to unveil all of 55 000 pages of the e-mails she turned over by January 29, 2016. But a federal judge this month chastised the department for moving too slowly in providing The Associated Press with thousands of e-mails submitted through the Freedom of Information Act.Republicans are pushing Clinton to turn her server over to a third party for forensic evaluation."Her poor judgment has undermined our national security, and it is time for her to finally do the right thing," said House Speaker John Boehner.Clinton spokesperson Nick Merrill said she had followed "appropriate practices in dealing with classified materials".But there's little dispute among intelligence officials that Clinton should have been more careful with her information - though her behaviour was likely not criminal.Current and former US intelligence officials say they assume that all of the e-mail that transited Clinton's home server is in the possession of Russian or Chinese intelligence services, who would have easily bypassed whatever security measures she took. They, too, spoke on condition of anonymity because they weren't authorised to discuss the Clinton email situation publicly.Whether a security violation or not, the risk for Democrats is that questions about her e-mail harden into an early narrative about Clinton's honesty and management skills. Already, Republicans have spent months depicting Clinton as a creature of Washington who flouts the rules for personal gain.Clinton's people say questions about her correspondence won't sway voters, who they argue are more focused on economic and family issues. But, there are signs that the issue may have already affected views of their candidate.An Associated Press-GfK poll released last week found that voters view her as less decisive and inspiring than when she launched her presidential campaign just three months ago. Just 3 in 10 said the word "honest" describes her very or somewhat well.