Following President Donald Trump’s “massive precision strikes” on Iran, U.S. officials are warning of potential cyber retaliation and attacks on infrastructure.

The Department of Homeland Security said Iran is likely to first retaliate against Israel but may also hit U.S. networks due to “their perception of U.S. support for Israeli strikes.” The Center for Internet Security added that “crude or escalatory tactics” could be used, especially if Iran’s direct capabilities are weakened. Iranian hackers have already infiltrated U.S. water and wastewater systems.

Iran’s proxy groups in the Middle East may target American interests abroad, although their reach inside the U.S. is limited. These groups, while less sophisticated, could still “disrupt public infrastructure and the private sector.”

There are also concerns about lone-wolf attacks by Shia-inspired extremists. A 2018 report warned that U.S. military action could trigger “Shia HVE \[homegrown violent extremist] activity relatively quickly.”

Iranian nationals have previously launched cyberattacks. One pleaded guilty to a ransomware attack on Baltimore in 2019. Others have been linked to assassination plots, with one targeting Trump and other U.S. officials. Officials urge critical infrastructure to increase security “immediately.”