The US Department of Health and Human Services was attacked by suspected foreign hackers as rumors swirled of a coronavirus-triggered national lockdown.

The attack flooded the HHS website with millions of hits Sunday night but failed to significantly slow the site.

Bloomberg News first reported the cyber assault, which resulted in no apparent theft of data.

Officials assume it’s the work of a foreign group, Bloomberg reported, spurring the White House National Security Council to issue a rare tweet late Sunday that “rumors of a national #quarantine are FAKE. There is no national lockdown.”

Vice President Mike Pence’s spokeswoman Katie Miller denied a CNN report Monday that a national curfew was under consideration in response to the COVID-19 outbreak. “That’s not even in the realm of things we’re asking governors for,” she said.

The White House’s official Twitter account said Monday, “Rumors of a national lockdown or national quarantine recently shared via text message are FAKE.”

It’s unclear if authorities have evidence to link the rumor and the cyber attack. US officials attributed previous politically motivated cyberattacks, some intended to influence US politics, to Russia, China, Iran and North Korea.

HHS spokeswoman Caitlin Oakley said in a statement that the incident is under investigation.

“On Sunday, we became aware of a significant increase in activity on HHS cyberinfrastructure and are fully operational as we actively investigate the matter,” Oakley said. “Early on while preparing and responding to COVID-19, HHS put extra protections in place. We are coordinating with federal law enforcement and remain vigilant and focused on ensuring the integrity of our IT infrastructure.”

NSC spokesman John Ullyot said, “HHS and federal networks are functioning normally at this time” and that “the federal government is investigating this incident thoroughly.”

The number of US COVID-19 cases passed 3,600 on Monday, with 61 deaths.