The Supreme Court ruled Thursday that Google must disclose the list of personal information it has shared with third parties, including United States intelligence.

In 2014, four South Korean activists filed a lawsuit against the global tech giant and its local unit, Google Korea, demanding to disclose the handling of their personal information.

Under South Korean law, online service providers must respond to a customer's request to disclose any record of their personal data being shared with a third party.

An appeals court had earlier partially sided with the plaintiffs but ruled that Google has the right to reject the demand on issues that can be kept private in accordance with the relevant U.S. laws.

The Supreme Court, however, partially overturned the previous rulings and sent the case back to the Seoul High Court for a retrial.

The highest court said even if personal information was provided to foreign intelligence agencies for probable cause, the service provider must notify the users of such acts when that cause terminates.

The plaintiff alleged Google passed on the private information of its users, including those that live outside the U.S., to an American government intelligence program known as PRISM.

PRISM trawls the internet for email and chat records of anyone who has contacts in the U.S. The program made global headlines after former U.S. intelligence contractor Edward Snowden divulged its existence.

"We plan to review the Supreme Court's decision carefully," Google Korea said in a press release, adding that protecting the privacy of its users is an important issue for the company.

Source: Yonhap News Agency