In July alone, hackers took over the Twitter accounts of U.S. politicians, stole terrabytes of coronavirus research and even infiltrated the U.K.’s Premier League soccer clubs. Can they cut off your electricity, too?

They’re trying. With millions of Americans now working from home — including the people who help keep the grid running — cyberattacks targeting the power sector have surged. In many cases, hackers use phishing emails to gain access to the computers of remote workers, looking to disable company systems for a ransom. But security experts warn that about dozen state-sponsored actors are also trying to infiltrate these networks.

The pandemic has created “a once in a lifetime opportunity to get access during a time of heightened remote access usage,” said Rob Lee, CEO at industrial security firm Dragos. “The bulk electric system is absolutely too important to allow adversaries access. It’s a matter of public safety as well as national security.”

Cyberattacks of all kinds have intensified during the COVID-19 pandemic, with hackers targeting public figures, banks, healthcare providers and others as the rise in remote work creates new access points. An assault on the power grid could have wide-ranging implications across sectors. While no outages have so far been attributed to hackers, grid companies are beefing up security amid an unprecedented onslaught that, in a worst case scenario, could trigger blackouts or damage vital equipment.

Even before the pandemic, hackers succeeded in infiltrating some energy infrastructure. In 2016, an Iran-based hacker gained remote access to an electric dam in New York for weeks. Earlier this year, ransomware shut down a natural gas facility for two days.