Story highlights The FBI put out a statement saying it was investigating

DNC Chairwoman Debbie Wasserman Schultz resigned on Sunday

Philadelphia (CNN) The Democratic National Convention was sent into upheaval over the weekend when Wikileaks released nearly 20,000 internal emails from the party -- some of which showed officials working against Sen. Bernie Sanders in the primary.

US officials suspect the email dump is the work of Russian hackers who were discovered in DNC servers earlier this year, and experts believe the coordinated release of the documents on the eve of the convention are an effort by Moscow to meddle in the US presidential election.

Here's what you need to know about the leak.

How do we know this is the work of Russia?

Cybersecurity experts who initially responded to the DNC hack identified two distinct groups of hackers operating in the system -- one who had exclusively gone after the party's opposition research file on Donald Trump, and one that had been snooping on DNC emails for about a year.

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