We’ll be reporting from Philadelphia all week and live-blogging each night. Check out all our dispatches from the Democratic convention here.

PHILADELPHIA — Robby Mook, Hillary Clinton’s campaign manager, said Sunday that Russian hackers broke into the Democratic Party’s email system in order to help Donald Trump by embarrassing the party. But there’s no hard proof of that theory, which is one of many that have arisen from a remarkable act of political espionage.

What we do know at this point is that there is a strong likelihood the hackers who penetrated the Democratic National Committee’s email system were Russian. Last month, security experts who studied the breach told several newspapers that it bore the hallmarks of Russian government hackers, based on the patterns of the intrusion and some of the data that the researchers discovered.

It was not clear, though, that the hacking was done at the behest of high-ranking Russian government officials, including President Vladimir Putin, or what its intended purpose was. That’s something the FBI will look into; the bureau announced Monday that it will investigate the breach.

The first theory floated, in mid-June, was that the hack was seeking intelligence about Trump. According to several intelligence experts, the Russian hackers wanted the DNC’s opposition research on Trump, because they didn’t have much information about him.

Russia was probably “scrambling to catch up, as they did not see him [Trump] as a viable political figure until this year,” said cybersecurity expert Brandon Valeriano, co-author of “Cyber War Versus Cyber Realities,” in an email. “Russia has legions of online hackers and spies, they have to do something. Collecting information on political opposition is their tradecraft.”

Steve Adler, who heads the political data research firm rVote and previously worked on another provider of technology to Democratic groups, NGP Van, agreed with that theory.

“The Russians don’t have a lot of spy data on Trump because he’s new to the political arena,” he said by email.

The intrusion was claimed by someone with the nom-de-hack of “Guccifer 2.0,” but it’s not clear (though he claims to be a single individual born in Eastern Europe) who that really is. The name could even represent freelancers hoping to gain the favor of Russian officials, or one of the country’s official intelligence agencies. The Trump campaign has vociferously denied it was the beneficiary of the hack.

It seems likely that there more leaks to come from the hack. On ABC News, Donna Brazile, who will become interim chair of the DNC, said she thought more information would emerge via Wikileaks over the coming months, “because it was not a one-month breach or a two-month breach.”

Valeriano said the issue at hand is much larger than any one party or entity’s being hacked. It’s a sign of how one of the hallmarks of the modern era — networked, global access to information — is also an Achilles’ heel.

“That such important and potentially damaging information is online and accessible from an off-site location like Russia demonstrates the severe problem we have with cybersecurity,” Valeriano said. “In making things easier and allowing for global collaboration, our secrets are now in the hands of the opposition.”





FiveThirtyEight: Day 1 of the Democratic National Convention