Highly sensitive personal information used in the security vetting of top government officials is being transported by commercial couriers and held by private contractors with patchy cyber security, sparking concerns about the risks of large-scale outsourcing of a system intended to safeguard national secrets.

The Australian Government Security Vetting Agency's processing of security clearances for officials has for years been plagued by delays, with the agency groaning under the weight of increased demand and a backlog of cases. The average wait time for the highest clearance level, known as "positive vetting", is sitting at almost 15 months.

In its efforts to slash the delays, the agency has enlisted 22 contractors who are now processing 85 per cent of assessments, according to evidence heard by a parliamentary committee in Canberra. At least 14 of the contractors are conducting positive vetting clearances, required by department secretaries, senior military officers, agency heads and other key officials who access top secret intelligence.

The Department of Defence headquarters in Canberra. Credit:Andrew Taylor

Security clearances are used to ensure officials can be trusted with classified information and are not vulnerable to blackmail and coercion by foreign intelligence agencies or criminal organisations. As part of the exhaustive positive vetting process, individuals must provide highly-detailed employment, financial, sexual, medical, psychological, family, drug and alcohol histories stretching back years.