The Chinese government espionage campaign that has deeply penetrated more than a dozen U.S. telecommunications companies is the “worst telecom hack in our nation’s history — by far,” a senior U.S. senator told The Washington Post in an interview this week.

The FBI has confirmed that Chinese hackers were responsible for a series of telecommunication breaches that may have lasted months.

All the major U.S. carriers, including AT&T, Verizon, and T-Mobile, were impacted, according to the Post. Incredibly, Warner says the hackers are still inside the U.S. system and there’s no obvious way to get them out that doesn’t involve physically replacing old equipment, according to Warner.

A breach of telecoms companies that the United States said was linked to China was the "worst telecom hack in our nation's history - by far", the chairman of the Senate Intelligence Committee told the Washington Post on Thursday.

Telecoms hack on US government officials is 'worst in nations history' and 'the barn door is still wide open' says senator