A federal grand jury indicted three Silicon Valley engineers on charges of stealing trade secrets from Google and other technology companies and transferring sensitive data to Iran, prosecutors said Thursday.

Samaneh Ghandali, 41, her sister Soroor Ghandali, 32, and Mohammadjavad Khosravi, 40 — all residents of San Jose — were arrested Thursday and appeared in a federal district court the same day.

The indictment identified the defendants as Iranian nationals. Soroor was in the U.S. on a nonimmigrant student visa. Samaneh later became a U.S. citizen, and Khosravi, her husband, became a U.S. legal permanent resident. Prosecutors said that Khosravi previously served in the Iranian army.

The trio faces charges of conspiracy to commit trade secret theft, theft and attempted theft of trade secrets, and obstruction of justice, according to the U.S. attorney's office for the Northern District of California.

Prosecutors alleged the three defendants exploited their positions at leading technology firms that develop mobile computer processors to obtain hundreds of confidential files, including materials related to processor security and cryptography.

Samaneh and Soroor worked at Google before joining a third company identified only as Company 3. Khosravi worked at a separate firm referred to as Company 2, which develops system-on-chip (SoC) platforms such as the Snapdragon series for smartphones and other mobile devices.

SoC is a semiconductor that integrates numerous components, such as graphics processing units and memory, into a power-efficient package. Common SoCs include Qualcomm's Snapdragon, found in most high-end Android phones, and Apple's A-series for iPhones.

In a statement to CNBC, Google said it had detected the alleged theft through routine security monitoring before referring the case to law enforcement.

"We have enhanced safeguards to protect our confidential information and immediately alerted law enforcement after discovering this incident," spokesman José Castañeda said.

The tech giant also pointed to measures to protect its trade secrets, including restricting employees' access to sensitive information, two-factor authentication for work-related Google accounts and logging file transfers to third-party platforms such as Telegram.

Authorities alleged the defendants routed stolen files through a third-party communications platform to channels bearing each of their first names, before copying the material to personal devices, each other's work devices, and to Iran.

"The method in which confidential data was transferred by the defendants involved deliberate steps to evade detection and conceal their identities," said FBI Special Agent in Charge Sanjay Virmani. 

The defendants sought to cover their tracks after Google's internal security systems flagged Samaneh's activity and revoked her access to company resources in August 2023.

According to the indictment, she signed an affidavit falsely claiming she had not shared Google's confidential information outside the company. During that period, a personal laptop linked to Samaneh and Khosravi was used to search for methods to delete communications and to research how long mobile carriers retain message records, prosecutors said.

The couple also allegedly photographed hundreds of computer screens containing confidential information from Google and Company 2, in what appeared to be an attempt at circumventing digital monitoring tools.

On the night before the pair traveled to Iran in December 2023, Samaneh allegedly took about 24 photos of Khosravi's work computer screen containing Company 2's trade secrets, including its Snapdragon SoCs.

Prosecutors allege that while in Iran, a device linked to Samaneh accessed those photographs, while Khosravi accessed additional Company 2's proprietary information, such as Snapdragon SoC hardware architecture.

Prosecutors said in the indictment that Snapdragon SoC trade secrets had independent economic value because they were not generally known and could not be readily obtained from Company 2's competitors, who could benefit from their disclosure or use.

If convicted, each defendant faces up to 10 years in prison for each trade secret charge and up to 20 years for obstruction of justice, along with fines of up to $250,000 per count.