— -- Hackers are claiming to have released the personal information of nearly all Democrats in the U.S. House of Representatives, including members' private cell phone numbers and email addresses.
The FBI is looking into the matter, with officials suspecting that Russian hackers are behind the cyberattack on Democratic organizations that came to public attention late last month.
The Democratic Congressional Campaign Committee's (DCCC) national press secretary Meredith Kelly told ABC News that the committee is aware of reports that sensitive information belonging to congressional Democrats has been leaked.
The alleged leak comes after the campaign committee told ABC News in late July it had been “the target of a cybersecurity incident,” just weeks after the Democratic National Committee also revealed it was hacked.
“As previously noted, the DCCC has been the target of a cybersecurity incident, and we are cooperating with federal law enforcement in their ongoing investigation. We are aware of reports that documents claimed to be from our network have been released and are investigating their authenticity,” Kelly said in a statement to ABC News late Friday.
House Minority Leader Nancy Pelosi, the highest-ranking Democrat in Congress, sent a letter to party members on Saturday, calling the incident an "electronic Watergate."
"As you are aware, the DCCC and other Democratic Party entities have been the target of cybersecurity intrusions -- an electronic Watergate break-in," Pelosi wrote. "As of last night, a mix of personal and official information of Democratic Members and hundreds of congressional staff, purportedly from a hack of the DCCC, was posted online."
Pelosi said she was among those whose phone number was leaked. She said she is changing her number and urged her Democratic colleagues to do the same.
"On a personal note, I was in the air flying from Florida to California when the news broke. Upon landing, I have received scores of mostly obscene and sick calls, voicemails and text messages," she wrote. "This is a sad course of events, not only for us, but more importantly for our country."
The House Democratic Caucus also sent a notice to its members early Saturday morning advising them to change the passwords to all their email accounts, even personal ones, and "to strongly consider changing passwords associated with sensitive personal accounts such as banking institutions."
Democratic Rep. Adam Schiff of California, ranking member of the House Intelligence Committee, said in a statement Friday night that releasing private information “is never acceptable.”
"The unauthorized disclosure of people's personally identifiable information is never acceptable, and we can fully expect the authorities will be investigating the posting of this information,” Schiff said. "I have every confidence that law enforcement will get to the bottom of this, and identify the responsible parties. And when they do, I hope the administration will disclose who is attempting to interfere with the American political process, and levy strong consequences against those responsible."
ABC News has reached out to several Democratic lawmakers’ offices to further verify the accuracy of reports of the leak.
An investigation into the cyberattack on the DCCC, the official campaign arm for House Democrats, is ongoing but investigators have said "this is similar to other recent incidents, including the DNC breach," Kelly said in a statement to ABC News in late July.
She said the campaign committee is working with federal law enforcement to further investigate the matter. The committee has also hired outside forensic experts at CrowdStrike to investigate.
CrowdStrike was the first to analyze the Democratic National Committee hack and brought in three independent cybersecurity firms to examine parts of malware that infected computers belonging to the party's national committee. In June, CrowdStrike identified two Russian hacker groups that the firm said were working for two rival Russian intelligence agencies.
Michael Buratowski, senior vice president of cybersecurity services at Fidelis Cybersecurity, investigated the DNC hack alongside Crowdstrike. He told ABC News that Russian hackers, typing on keyboards configured in Cyrillic and doing it in a time zone consistent with Moscow, created the “eloquent” code that breached computers belonging to the DNC.
“This was absolutely not an amateur operation … When you look at the totality of all those pieces and you put them together, it kind of paints a really good picture of who the actor was,” Buratowski said an interview in late July. “I come from a law enforcement background, and it’s [about being] beyond a reasonable doubt. And I would say it’s beyond a reasonable doubt … I’m very confident that the malware that we looked at [was from] Russian actors.”
“When we looked at the malware, we found that it was very, very eloquent in its design as well as its functionality -- very advanced, not something that script user or lower-level hacker would be able to really generate or customize,” he said.
ABC News’ Jordyn Phelps, Brian Ross, Lee Ferran, James Gordon Meek, Matthew Mosk, Rhonda Schwartz and Pierre Thomas contributed to this report.