WASHINGTON (AP) — Federal authorities on Tuesday urged telecommunication companies to boost network security following a sprawling Chinese hacking campaign that gave officials in Beijing access to private texts and phone conversations of an unknown number of Americans.

The guidance issued by the FBI and the Cybersecurity and Infrastructure Security Agency is intended to help root out the hackers and prevent similar cyberespionage in the future. Officials who briefed reporters on the recommendations said the U.S. still doesn't know the true scope of China's attack or the extent to which Chinese hackers still have access to U.S. networks.

In one sign of the global reach of China's hacking efforts, the government's warning was issued jointly with security agencies in New Zealand, Australia and Canada, members of the Five Eyes intelligence alliance, which also includes the U.S. and Britain.

Dubbed Salt Typhoon by analysts, the wide-ranging cyberespionage campaign emerged earlier this year after hackers sought to penetrate the networks of multiple telecommunications companies.

The hackers used their access to telecom networks to target the metadata of a large number of customers, including information on the dates, times and recipients of calls and texts.

The hackers succeeded in retrieving the actual audio files of calls and content from texts from a much smaller number of victims. The FBI has contacted victims in this group, many of whom work in government or politics, but officials said it is up to telecom companies to notify customers included in the first, larger group.

Despite months of investigation, the true scale of China’s operation, including the total number of victims or whether the hackers still have some access to information, is currently unknown.

The FBI has said some of the information targeted by the hackers relates to U.S. law enforcement investigations and court orders, suggesting the hackers may have been trying to access programs subject to the Foreign Intelligence Surveillance Act, or FISA. The law grants American spy agencies sweeping powers to surveil the communications of people suspected of being agents of a foreign power.

But on Tuesday, officials said they think the hackers were more broadly motivated, hoping to burrow deeply into the nation's telecommunications systems to gain wide access to Americans' information.

The suggestions for telecom companies released Tuesday are largely technical in nature, urging encryption, centralization and consistent monitoring to deter cyber intrusions. If implemented, the security precautions could help disrupt the Salt Typhoon operation and make it harder for China or any other nation to mount a similar attack in the future, said Jeff Greene, CISA's executive assistant director for cybersecurity and one of the officials who briefed reporters Tuesday.