In the wake of President Donald Trump's "massive precision strikes" on Iran, concerns have been raised both for Americans in the region and at home.
A principal area of worry is cyberattacks by Iranian state actors, including targeting the banking system or energy grid.
A recent Department of Homeland Security bulletin warned: "Iranian government-affiliated cyber actors will probably prioritize retaliatory attacks against Israeli targets in the short term but may target U.S. networks due to their perception of U.S. support for Israeli strikes."
The bulletin urged domestic critical infrastructure entities to "immediately" assess and shore up their security. Such attacks have already infiltrated U.S. water and wastewater systems, according to the non-profit think tank Center for Internet Security, which briefed law enforcement on Friday.
The Center was also concerned that Iran, in the wake of Israeli military strikes, might use "crude or escalatory tactics" or informal networks if its capabilities were degraded.
"The likelihood of such attacks will increase if the U.S. strikes Iran or overtly provides military support to the Israeli air campaign," the group said.
And the Center assessed that Iran's considerable network of proxy groups might be able to strike U.S. interests in the Middle East, though their capacity to strike the U.S. homeland was more limited.
The groups, they assessed, while less sophisticated, could still disrupt public infrastructure and the private sector.
On top of that was the fear of attacks by foreign nationals or American citizens inspired to strike the U.S.
In 2018, the National Counterterrorism Center issued a report saying Iran-sponsored or Shia-inspired -- referring to one of the two major branches of Islam which is dominant in Iran -- terror on the U.S. homeland is unlikely, except if the U.S. were to attack Iran.
"Given sustained bilateral U.S.-Iran tensions, the occurrence of such a catalyst could prompt Shia HVE [homegrown violent extremist] activity relatively quickly, underscoring the benefits of early engagement with Shia communities about indicators of HVE radicalization. Potential triggering events for such Shia HVE violence include U.S. military action against Iran."
Iranian forces themselves have previously targeted American interests, hitting U.S. bases in the Middle East, for instance, after top Islamic Revolutionary Guard Corps commander Gen. Qassem Soleimani was killed in an American airstrike in Iraq in 2020.
Iranian nationals have also carried out major cyberattacks.
An Iranian national pleaded guilty last month to helping orchestrate the 2019 Baltimore, Maryland, ransomware attack that caused tens of millions of dollars in damage and disrupted critical city services. While prosecutors did not allege Sina Gholinejad was directed in his activities by the Iranian government, in announcing the case they warned more broadly of Iranian government-backed hacking groups targeting U.S. critical infrastructure.
And in the summer of last year, the Justice Department also separately charged a Pakistani man with ties to the Iranian government for allegedly seeking to carry out political assassinations. Authorities told ABC News that among Asif Merchant's targets were Trump and other current and former U.S. officials.