BAE Systems has been confirmed as the company, after the loss of documents was revealed in Senate estimates hearings yesterday where the company was not named.
The security manual remains missing and parliamentary officials were not told about it until three months after it happened.
The Senate estimates hearing was reassured that around half the manual comprised publicly available material, while other parts were redundant or had been modified in recent months.
A statement from BAE Systems Australia said, "Following identification of the security incident, we conducted a thorough investigation and are confident that we have the processes and procedures in place to avoid the possibility of an incident of this nature happening in the future.
"We also understand that there has been no compromise to the security of Parliament House."
The Department of Parliamentary Services conducted an independent review of the incident, with BAE Systems required “to re-assess its document-handling procedures”.
Over the last few years, BAE Systems Australia has landed several contracts outside of Defence contracts. Some of these contracts include dealing with security cameras and digital broadcasting at Parliament House.
BAE Systems (UK) is currently bidding for the $35 billion Future Frigate Project against Spain's Navantia and Italy's Fincantieri.
BAE Systems Australia is also competing for the $5 billion LAND 400 Phase 2 Project and Project AIR 2025 Phase 6 Jindalee Operational Radar Network.