The chairman of the Senate Intelligence Committee said on Thursday that China’s recent breach of the inner workings of the US telecommunications system went much deeper than the Biden administration has described. The chairman said hackers can listen to telephone conversations and read text messages.

“The warehouse door is still open, or mostly open,” the Democratic chairman, Sen. Mark Warner of Virginia, a former telecommunications executive, said in an interview Thursday.

Mr Warner said he was stunned by the scope and depth of the breach, which was carried out last year by a group linked to Chinese intelligence that has been named. Salt Typhoon From Microsoft, whose cybersecurity team discovered the hack over the summer. Government officials are struggling to understand what China achieved and how it could monitor the conversations of several well-connected Americans, including President-elect Donald J. Trump and Vice President-elect J.D. Vance.

At first, the FBI and other investigators believed the Chinese hackers used stolen passwords mostly on a system that taps telephone conversations and texts under court orders. It is managed by several of the country’s telecommunications firms, including the three largest – Verizon, AT&T and T-Mobile. But in recent days, investigators have discovered just how deep China’s hackers had moved across the country, exploiting aging equipment and seams in the networks connecting disparate systems.

Since the hack was revealed, the Chinese infiltrators have apparently disappeared, suspending their intrusion so their full activity remains undetected, U.S. officials said. But Mr. Warner said it would be wrong to conclude that the Chinese had been kicked out of the country’s telecommunications system, or that investigators even understood how deeply embedded they were.

“We haven’t found them everywhere,” Mr Warner said.

The committee has received briefings from the government on the hack, and Mr Warner has spoken with telecommunications executives.