The United States is on high alert for cyberattacks on its financial and infrastructure computer systems after Iran vowed "forceful revenge" following last week's targeted killing of a senior military commander.

"Iran maintains a robust cyber-program and can execute cyberattacks against the United States," the US Department of Homeland Security warned in a bulletin issued after a drone attack on Jan 3 killed Qasem Soleimani, a major-general in the Islamic Revolutionary Guard Corps and commander of its Quds Force.

"Iran is capable, at a minimum of carrying out attacks with temporary disruptive effects against critical infrastructure in the United States. An attack on the homeland may come with little or no warning."

The US Cybersecurity and Infrastructure Security Agency said sophisticated cyberattacks typically seek to steal vital information and disrupt or destroy the delivery of essential services such as water, electricity and transportation.

"It's hard to predict what the retaliation might look like despite all the statements being made," Holly Dagres, a nonresident fellow at the Atlantic Council and editor of IranSource blog, told Newsweek. "One thing to remember is that Iran is a calculating, rational state and not suicidal. They traditionally play by the rules of asymmetrical warfare."

"While we don't expect cyberattacks to cripple our society, it's far more likely that they will score some major blows against individual companies," John Hultquist, senior director of intelligence analysis for FireEye, a Milpitas, California-based cybersecurity firm, told China Daily. "The US' vastly superior intelligence and military capability won't be absorbing cyberattacks from Iran. It will be our incredibly complex, technology-reliant economy."

Cyberattacks can be mounted from anywhere in the world, and it's often hard to identify the source, especially if attackers mask their identities by adopting a false cover. Analysts said the likelihood of cyberattacks from Iran underscores the obvious: Its military can't match the skill and technology of US forces.

Iran has apparently mounted successful cyberattacks in the past. In 2011, hackers attacked computers at the New York Stock Exchange and Nasdaq Stock Market.

Iran also has been the target of successful cyberattacks. The Stuxnet virus, discovered in 2010 and believed to have been the work of US and Israel, disrupted uranium enrichment at Iran's nuclear plant near Natanz. The virus reportedly caused Iran's centrifuges to spin out of control and destroyed about 20 percent of the equipment. Iran then reportedly built its own cyberattack capability.

"Iran will definitely use everything they have at their disposal eventually, but I don't think a major cyberattack right this second makes sense," Jake Williams founder of Rendition Infosec, a cybersecurity firm based in Augusta, Georgia, and a former National Security Agency official, told The Washington Post on Sunday. "Every piece of malware Iran uses now removes a bullet they can fire later to have a greater effect."