The Internet company used by Hillary Clinton to maintain her private server was sued for stealing dozens of phone lines including some which were used by the White House.
Platte River Networks is said to have illegally accessed the master database for all US phone numbers.
It also seized 390 lines in a move that created chaos across the US government.
Among the phone numbers which the company took – which all suddenly stopped working – were lines for White House military support desks, the Department of Defense and the Department of Energy, a lawsuit claims.
Others were the main numbers for major financial institutions, hospitals and the help desk number for T2 Communications, the telecom firm which owned them.
A lawsuit filed on behalf of T2 claims that the mess took 11 days to fix and demands that Platte River pay up $360,000 in compensation.
The claims raise questions about the competence of Platte River, which is based in Denver, Colorado, to handle Mrs Clinton’s highly sensitive personal information while she was Secretary of State.
The Secretary of State’s emails would have been potentially a target for foreign espionage.
Mrs Clinton installed the system at her home in Chappaqua, upstate New York, and did not even have an official email address until the year she left office.
Earlier this week it emerged that she has handed over the server to the FBI which is investigating her and a number of her top aides.
Mrs Clinton acted after the Inspector General for the intelligence community said that he had found four emails that were stored on it were classified and two of those were Top Secret, the highest level of classification.
Until now Mrs Clinton has insisted that none of the emails were classified at the time she sent or received them.
The lawsuit was filed by T2 in November last year and relates to a deal that went through in June.
By that time Mrs Clinton has left her post as Secretary of State; she was in office between 2009 and 2013.
T2 alleges that it had provided 16 phone lines to an insurance broker called Cambridge until they decided to switch providers and signed up with Windstream Communications, who worked with McLeod USA, a local exchange carrier owned by Windstream, and Platte River.
But instead of taking over the 16 lines, T2 claims that the companies asked for 390 more lines in what they called ‘intentional misappropriation’.
T2 alleges that they did this by illegally accessing the database for the Number Portability Administration Centre, the master agency which manages all US phone numbers.
Read more: dailymail.co.uk