The U.S. carried out the cyber operations with the goal of undermining Iran's capabilities to spread "propaganda", two U.S. officials told Reuters on the condition of anonymity.
One of the officials said the strike affected physical hardware, but they did not provide further details.
The Pentagon declined to comment about the operation.
Tensions in the region have been high for months, following US President Donald Trump's decision to impose crushing sanctions that target Iran's crude oil sales and have crippled its economy.
Last month, two Saudi oil facilities were attacked, temporarily halving the kingdom's crude output and setting oil markets alight. The Iran-aligned Houthi militant group in Yemen claimed responsibility.
Lewis added it may not be possible to deter Iranian behaviour with even conventional military strikes.
It was unclear whether there have been other USA cyber attacks since the one in late September.
The ISI DG, who in the last week of September quietly visited Iran and Saudi Arabia, is believed to have played a major role in laying the ground for de-escalation in the Middle East. Officials said he would be the focal person for future contacts between Saudi Arabia and Iran.
Rouhani said that Iran had a video showing "a number of missiles" fired at the tanker, with two hitting the tanker itself, according to the Iranian IRNA news agency.
Previous year a Reuters investigation found more than 70 websites that push Iranian propaganda to 15 countries, in an operation that cybersecurity experts, social media firms and journalists are only starting to uncover.
Iran's President Hassan Rouhani warned Sunday it would be "a big mistake" to think his country won't respond to threats after the alleged attack.
If confirmed, the Sabiti would be the first Iranian ship to have been targeted since a spate of attacks on vessels in the Gulf that Washington blamed on Tehran.
Though Saudi Arabia's geographic proximity to the incident means it could have carried out the attack, initial reports suggest Saudi officials were scrambling to determine the extent of the damage, including its environmental fallout, and trying to determine if Iran had launched a false-flag operation to justify attacks on Saudi infrastructure along its Red Sea coast.