Several U.S. federal government agencies have been hit in a global cyberattack by Russian cybercriminals that exploits a vulnerability in widely used software, according to a top U.S. cybersecurity agency.The U.S. Cybersecurity and Infrastructure Security Agency “is providing support to several federal agencies that have experienced intrusions affecting their MOVEit applications,” Eric Goldstein, the agency’s executive assistant director for cybersecurity, said in a statement on Thursday to CNN, referring to the software impacted. “We are working urgently to understand impacts and ensure timely remediation.”Aside from U.S. government agencies, “several hundred” companies and organizations in the U.S. could be affected by the hacking spree, a senior CISA official told reporters later Thursday, citing estimates from private experts.Clop, the ransomware gang allegedly responsible, is known to demand multimillion-dollar ransoms. But no ransom demands have been made of federal agencies, the senior official told reporters in a background briefing.CISA’s response comes as Progress Software, the U.S. firm that makes the software exploited by the hackers, said it had discovered a second vulnerability in the code that the company was working to fix.The Department of Energy is among multiple federal agencies breached in the ongoing global hacking campaign, a department spokesperson confirmed to CNN.The hacks have not had any “significant impacts” on federal civilian agencies, CISA Director Jen Easterly told reporters, adding that the hackers have been “largely opportunistic” in using the software flaw to break into networks.The news adds to a growing tally of victims of a sprawling hacking campaign that began two weeks ago and has hit major U.S. universities and state governments. The hacking spree mounts pressure on federal officials who have pledged to put a dent in the scourge of ransomware attacks that have hobbled schools, hospitals and local governments across the U.S.Since late last month, the hackers have been exploiting a flaw in widely used software known as MOVEit that companies and agencies use to transfer data. Progress Software, the US firm that makes the software, told CNN Thursday that a new vulnerability in the software had been discovered “that could be exploited by a bad actor.”“We have communicated with customers on the steps they need to take to further secure their environments and we have also taken MOVEit Cloud offline as we urgently work to patch the issue,” the company said in a statement.Agencies were much quicker Thursday to deny they’d been affected by the hacking than to confirm they were. The Transportation Security Administration and the State Department said they were not victims of the hack.The Department of Energy “took immediate steps” to mitigate the impact of the hack after learning that records from two department “entities” had been compromised, the department spokesperson said.“The Department has notified Congress and is working with law enforcement, CISA, and the affected entities to investigate the incident and mitigate impacts from the breach,” the spokesperson said in a statement.One of the Department of Energy victims is Oak Ridge Associated Universities, a not-for-profit research center, a department spokesperson told CNN. The other victim is a contractor affiliated with the department’s Waste Isolation Pilot Plant in New Mexico, which disposes waste associated with atomic energy, the spokesperson said.Federal News Network first reported on the Department of Energy victims.Johns Hopkins University in Baltimore and the university’s renowned health system said in a statement this week that “sensitive personal and financial information,” including health billing records may have been stolen in the hack. Video below: ID theft expert sheds light on data breachesMeanwhile, Georgia’s state-wide university system – which spans the 40,000-student University of Georgia along with over a dozen other state colleges and universities – confirmed it was investigating the “scope and severity” of the hack.CLOP last week claimed credit for some of the hacks, which have also affected employees of the BBC, British Airways, oil giant Shell, and state governments in Minnesota and Illinois, among others.The Russian hackers were the first to exploit the MOVEit vulnerability, but experts say other groups may now have access to software code needed to conduct attacks.The ransomware group had given victims until Wednesday to contact them about paying a ransom, after which they began listing more alleged victims from the hack on their extortion site on the dark web. As of Thursday morning, the dark website did not list any U.S. federal agencies. Instead, the hackers wrote in all caps, “If you are a government, city or police service do not worry, we erased all your data. You do not need to contact us. We have no interest to expose such information.”The CLOP ransomware group is one of numerous gangs in Eastern Europe and Russia that are almost exclusively focused on wringing their victims for as much money as possible.“The activity we’re seeing at the moment, adding company names to their leak site, is a tactic to scare victims, both listed and unlisted, into paying,” Rafe Pilling, director of threat research at Dell-owned Secureworks, told CNN.