U.S. officials said Tuesday they had not expelled Chinese hackers from telecommunications companies, warning concerned users to turn to encrypted messages.

The U.S. has been investigating the Salt Typhoon hackers since late spring and early summer this year, a senior FBI official said.

Officials from the FBI and the Cybersecurity and Infrastructure Security Agency say the major Chinese hack began in late spring, and they are strongly urging Americans to use encrypted communications.

U.S. government officials said Tuesday that the China-backed hacking group dubbed Salt Typhoon are still inside some of the networks of America's largest phone and internet providers, weeks after the long-running hacking campaign first came to light.

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.

US officials are still trying to help major telecom providers evict Chinese government-backed hackers from their networks and don’t have a timeline for when that will be done, officials said Tuesday.

China-linked spies are still lurking inside U.S. telecommunications networks roughly six months after American officials started investigating the intrusions, senior officials told reporters Tuesday.