Sam Curry, the chief security officer at Cybereason, a Boston-based computer security firm founded by three former members of Unit 8200, the Israeli military’s storied cyber warfare wing, said an Iranian cyberattack could come in various shapes and sizes. As with any form of asymmetric warfare, not knowing where the strike will land is the real issue, he said.

“They’re not going to start developing now the attacks that they’ll use, they have developed them already,” Curry told Quartz. “It could be military, could be civilian—the initiative now lies with Iran to pick and choose among the options they have. Will they retaliate in kind? Send a message of escalation? The question is, what and where and when?”

The United States has carried out its own cyberattacks against Iran. In 2010, a malware attack known as Stuxnet, which experts believe was jointly developed by the United States and Israel, destroyed one thousand centrifuges at Iran’s Natanz nuclear research facility.

Chris Morales, head of security analytics at Vectra, a California-based provider of technology that applies AI to detect and hunt for cyber attackers, said the United States and Iran have long been engaged in some degree of cyber warfare.

“Iran has identified cyber capabilities as part of their attack strategy a decade ago and have slowly been building up capabilities since they were hit with Stuxnet,” he said.

As a result, the global cybersecurity community is on high alert, Curry said, adding that he hopes the United States has not just given Iran a casus belli, or a “cause for war.”

“An escalating conflict would be a very bad way to start 2020,” he said.

Acting Department of Homeland Security secretary Chad Wolf said in a statement Friday that the agency was preparing for possible responses from Iran.

“The entire department remains vigilant and stands ready, as always, to defend the Homeland,” Wolf said. A spokesperson for US secretary of state Mike Pompeo, meanwhile, said the the United States remained committed to de-escalating the conflict with Iran.

Alireza Miryousefi, a spokesperson for Iran’s mission to the United Nations in New York City, did not respond to a request for comment.

📬 Sign up for the Daily Brief

Our free, fast, and fun briefing on the global economy, delivered every weekday morning.