By John Walcott, Joseph Menn and Mark Hosenball

WASHINGTON (Reuters) – Some U.S. intelligence officials suspect that Russian hackers who broke into Democratic Party computers may have deliberately left digital fingerprints to show Moscow is a “cyberpower” that Washington should respect.

Three officials, all speaking on condition of anonymity, said the breaches of the Democratic National Committee (DNC) were less sophisticated than other cyber intrusions that have been traced to Russian intelligence agencies or criminals.

For example, said one official, the hackers used some Cyrillic characters, worked during Russian government business hours but not on Russian religious or political holidays.”Either these guys were incredibly sloppy, in which case it’s not clear that they could have gotten as far as they did without being detected, or they wanted us to know they were Russian,” said the official.

Private sector cyber security experts agreed that the evidence clearly points to Russian hackers but dismissed the idea that they intentionally left evidence of their identities.

These experts – who said they have examined the breach in detail – said the Cyrillic characters were buried in metadata and in an error message. Other giveaways, such as a tainted Internet protocol address, also were difficult to find.

Russian hacking campaigns have traditionally been harder to track than China’s but not impossible to decipher, private sector experts said. But the Russians have become more aggressive and easier to detect in the past two years, security experts said, especially when they are trying to move quickly.

False flags have grown more common, but the government and private experts do not believe that is involved in the DNC case.

The two groups of hackers involved are adept at concealing their intrusions, said Laura Galante, head of global threat intelligence at FireEye, whose Mandiant subsidiary conducted forensic analysis of the attack and corroborated the findings of another cyber company, CrowdStrike.

Russian officials have dismissed the allegations of Moscow’s involvement as absurd. Russian Foreign Minister Sergei Lavrov, in his only response to reporters, said: “I don’t want to use four-letter words.”

EMBARRASSING EMAILS

While private cyber experts and the government were aware of the political party’s hacking months ago, embarrassing emails were leaked last weekend by the WikiLeaks anti-secrecy group just as the Democratic Party prepared to anoint Hillary Clinton as its presidential candidate for the Nov. 8 election.

DNC chairwoman, Debbie Wasserman Schultz, resigned after the leaked emails showed party leaders favoring Clinton over her rival in the campaign for the nomination, U.S. Senator Bernie Sanders of Vermont. The committee is supposed to be neutral.

The U.S. intelligence officials conceded that they had based their views on deductive reasoning and not conclusive evidence, but suggested Russia’s aim probably was much broader than simply undermining Clinton’s campaign.

They said the hack fit a pattern of Russian President Vladimir Putin pushing back on what he sees as the United States and its European allies trying to weaken Russia.

“Call it the cyber equivalent of buzzing NATO ships and planes using fighters with Russian flags on their tails,” said one official.

Two sources familiar with Democratic Party investigations into the hacking said the private email accounts of Democratic Party officials were targeted as well as servers.

They said that the FBI had advised the DNC that it was looking into the hacking of the individual officials’ private accounts. They also said the FBI also requested additional information identifying the personal email accounts of certain party officials.

The DNC hired CrowdStrike to investigate the hack. It spent about six weeks, from late April to about June 11 or 12, monitoring the systems and watching while the hackers – who they believed were Russian – operated inside the systems, one of the sources said.

What actions, if any, the Obama administration will take are unclear and could depend on what diplomatic considerations may ultimately be involved, a former White House cyber security official said.

In past cases, administration officials have decided to publicly blame North Korea and indict members of China’s military for hacking because the administration decided that the net benefit of public shaming – and increased awareness brought to cyber security – outweighed potential risks, the former official said.

But “the Russia calculation is far more difficult and precarious,” the former official said. “Russia is a much more aggressive, capable foreign actor both in the traditional military sense and in the cyber realm” and that made public attribution or covert retaliation much less likely.

The former official, and a source familiar with the Democratic Party investigations, said that they also were unaware of any U.S. intelligence clearly demonstrating that WikiLeaks had received the hacked materials directly from Russians or that WikiLeaks’ release of the materials was in any way directed by Russians.

(Reporting By John Walcott, Joseph Menn and Mark Hosenball; Additional reporting by Dustin Volz; Editing by David Rohde and Grant McCool)