Israel was able to track and target senior Iranian political and military leaders and nuclear scientists during the June war between the countries by hacking and tracking the phones of their bodyguards and drivers, the New York Times reported Saturday.

In its opening strikes on Iran in the early hours of June 13, Israel swiftly killed multiple top generals and nuclear scientists, among them Revolutionary Guards chief Maj. Gen. Hossein Salami, Armed Forces chief Maj. Gen. Mohammad Bagheri, and missile chief Brig. Gen. Amir Ali Hajizadeh, stunning and paralyzing Iran for long hours.

The Times report, which quoted several senior Iranian and Israeli military and intelligence officials, said that though top Iranian leaders were aware of the security threat posed by smartphones and avoided using them, this instruction did not extend to their security detail, enabling Israel to track and eliminate them.

“We know senior officials and commanders did not carry phones, but their interlocutors, security guards and drivers had phones; they did not take precautions seriously and this is how most of them were traced,” Sasan Karimi, a former deputy vice president for strategy in Iran’s government, told The Times.

The Times noted that Iran had been aware of Israel’s plan to kill top officials and had boosted their security. In doing so, it unwittingly allowed Israel to track and target the senior officials.

It further said that multiple guards were careless with their phone use prior to the war, posting updates about their doings on social media, further assisting Israel’s information-gathering efforts.

“Using so many bodyguards is a weakness that we imposed on them, and we were able to take advantage of that,” one Israeli defense official said.

After that first devastating blow, bodyguards were ordered to carry only walkie-talkies while on the job.

However, in at least one case, guards violated the orders allowing Israel to again target leaders, the report said, leading to a strike on a bunker during a secretive meeting of Iran’s Supreme National Security Council. President Masoud Pezeshkian was injured in the leg during that June 16 incident, but none of the top officials were killed, though a number of guards were.

“The enemy gets the majority of its intelligence through technology, satellites and electronic data,” the new head of the Revolutionary Guards Corps, Brig. Gen. Ahmad Vahidi said. “They can find people, get information, their voices, images and zoom in with precise satellites and find the locations.”

Israel said after the 12-day conflict that it had killed dozens of senior security officials and at least 11 senior nuclear scientists during the campaign. It was considered the worst blow to the Islamic Republic since the 1980s war with Iraq.

Iran retaliated to Israel’s strikes with barrages of missiles and drones that killed dozens. A ceasefire was reached on June 24 after Iran’s nuclear and ballistic missile programs were severely damaged.

Since the war, Iran, shaken by the level of Israeli penetration of its ranks, has engaged in a sweeping arrest and interrogation campaign of suspected spies and has executed a number of people accused of doing so. Israel has not commented on such cases.

At the same time, The Times cited Vahidi as telling Iranian media that though Israel did use human intelligence, most of its data-gathering was through electronic means.

“The enemy gets the majority of its intelligence through technology, satellites and electronic data,” Vahidi said. “They can find people, get information, their voices, images and zoom in with precise satellites and find the locations.”

Israel said its sweeping assault on Iran’s top military leaders, nuclear scientists, uranium enrichment sites, and ballistic missile program was necessary to prevent the Islamic Republic from realizing its avowed plan to destroy the Jewish state.

Iran has consistently denied seeking to acquire nuclear weapons. However, it enriched uranium to levels that have no peaceful application, obstructed international inspectors from checking its nuclear facilities, and expanded its ballistic missile capabilities. Israel said Iran had recently taken steps toward weaponization.

Current and former Israeli officials have said the offensive was the culmination of years of work by Mossad and Military Intelligence to build up intelligence capabilities to enable the elimination of targets with such precision.

Israel has warned it could resume its campaign should Iran attempt to rebuild its nuclear and missile programs.

International actors have sought since the ceasefire to reach an agreement with Tehran regarding the nuclear program, but have made little progress. On Thursday, Britain, France and Germany, known as the E3, triggered the so-called snapback mechanism to reinstate UN sanctions on Tehran for failing to comply with commitments made in a 2015 deal over its nuclear program. Iran has threatened to retaliate.

Efforts to reach an agreement are ongoing.