Iran has promised "a forceful revenge" in response to the US-ordered drone strike that killed Maj. Gen. Qassem Soleimani, the head of Iran's elite Quds Force, late Thursday.

Cybersecurity experts said that Iran had spent years establishing itself as an "intelligent cyber opponent" and was likely to leverage cyberattacks against the US.

Iran has been linked to cyberattacks against Turkey, Israel, the US, and the UK.

Cyberattacks could target internet infrastructure, online banks, or even the US power grid.

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Iran's leaders on Friday vowed to exact "a forceful revenge" against the US in response to the American drone strike that killed Maj. Gen. Qassem Soleimani, the head of Iran's elite Quds Force, late Thursday.

Now, cybersecurity and defense experts are bracing for an Iranian cyberoffensive that could target online infrastructure across the US military and the private sector.

Experts told Business Insider that Iran had spent years building out its computer-warfare capabilities. Since 2010, when Iran faced a cyberattack on its nuclear facilities, the country has focused heavily on beefing up its defense operations.

"Iran is an intelligent cyber opponent with an army of people testing our systems every minute of every day. It is the ultimate game of cat and mouse," Sam Curry, the chief security officer at Cybereason, told Business Insider.

However, the US has also focused heavily on building up its cyber defenses, said Kiersten Todt, a cybersecurity adviser in the Obama administration and the managing director of the Cyber Readiness Institute.

"I absolutely think that they will look to attack our critical infrastructure on the homeland," Todt told Business Insider, adding that, however, "our capabilities and our preparedness for that type of attack is strong, and our military is extremely well prepared for this."

US defense efforts will also be bolstered by a recent leak of Iran's cyber operations on a dark-web server, according to Charity Wright, a former National Security Agency analyst who is now a cyber-threat analyst at IntSights.

"These types of attacks could be devastating if the target is ill-equipped with proper defense," Wright said. "However, recent disclosures about how Iranian cyber groups operate has left them scrambling to change tactics and cover past operations. This does give Iranian opposition an advantage."

Here's what we know about Iran's capacity for online warfare and what a cyberattack could look like.