Dozens of U.S. intelligence, law enforcement, and cybersecurity agencies are closely monitoring America’s vast election infrastructure for any cyberattacks or other forms of disruption by foreign adversaries, but Election Day itself marks only the half-way point in such vigilance, the top U.S. cybersecurity official said.

“Today, in some senses is halftime,” Christopher Krebs, director of the Cybersecurity and Infrastructure Security Agency said in a news conference on Tuesday. “There may be other events or activities or efforts to interfere and undermine confidence in the election.”

With more than 100 million Americans having cast their ballots in early voting before Election Day, the final tally may exceed 150 million votes by the time polls close in Alaska and Hawaii, well past midnight on the U.S. east coast. But with a significant number of voters having cast their votes by mail, counting those could take a week or more, and even longer if one factors in legal challenges by both parties.

With no basis in fact, President Donald Trump and his advisors have said that a prolonged count would lead to fraud. In reality each state has a different deadline for certifying the final tally that ranges from 48 hours after Election Day to as late as 22 days after polls close. And the vast majority of states continue to count ballots, such as absentees, in the days after Nov. 3.

Chad Wolf, the acting secretary of the Department of Homeland Security, said that Americans should wait for official results to be announced. “I’d ask all Americans to be patient and to treat all sensational and unverified claims with skepticism.”

Election technology, like any piece of electronic equipment, can fail even without a cyberattack, a senior CISA official said on a conference call with reporters, pointing to an announcement from Frank La Rose, Ohio’s Secretary of State, that the state’s Franklin County was switching to paper poll books because of a technical glitch in their electronic ones. Poll books are used to verify voters’ identities before they cast a ballot.

[High early turnout of voters eases tech and security worries on Election Day]

Social media platforms as well as messaging apps can be conduits for disinformation, too, officials noted.

So, too, can telephones. Voters in at least six states are said to have received robocalls and texts today telling them to stay home because of COVID-19 and the FBI is investigating the calls, a senior official at CISA told reporters in its midday briefing.

Robocalls are not unusual on Election Day but they constitute a form of voter intimidation and vote suppression effort, the official said.

Some Chinese-Americans are said to be receiving messages on WeChat, a messaging platform, warning them that protests are being organized and trying to instill fear in voters.

A CISA official said U.S. officials were aware of such messages and have passed on the information to social media companies to address them.

CISA will continue to update its rumor vs. reality webpage to push back on domestic and foreign disinformation efforts, officials said.

The official said that the agency is closely monitoring attempts by foreign adversaries, especially Russia, to break into U.S. election infrastructure. The Pentagon’s U.S. Cyber Command has expanded its “hunt forward” mission to aid in that effort, the official said.

During the 2018 midterm election the U.S. Cyber Command sent cyber sleuths to Macedonia, Montenegro, and Ukraine to identify Russian intelligence networks as well as tools the Kremlin might use against the United States.

Those efforts by the Cyber Command have been expanded to help identify tactics and tools that the Iranians and the Chinese might use, the New York Times has reported.

The expanded scouting helps identify potential malware adversaries may use and that’s then shared with state election officials and private companies to look for those in U.S. election systems, the CISA official said.

The agency’s election monitoring hub that has been in operation for the past 40 days may well continue to operate for another 45 days, officials said.