Australia's Defence Department has stepped up an investigation into the theft of a departmental notebook computer from the hotel room of an Australian naval officer attending a defence seminar in Bangkok.

The officer, Peter de Maskens, a lieutenant commander and signals specialist in the Royal Australian Navy, was attending a week-long seminar, starting on July 4 and overseen by the Thai armed forces, on regional security issues.

Intelligence sources said there are concerns other foreign intelligence services, in particular China and Burma, may have attempted to track down the stolen computer.

De Maskens, who was awarded an Order of Australia medal this year, is an expert in the field of maritime communications and information systems.

A Thai police report said de Maskens had left his five-star Banyan Tree Hotel at 2am, travelling to the red light entertainment district of Nana Plaza in Sukhumvit Road. He returned to the hotel accompanied by a Thai person just before 3am.

The report said de Maskens appeared drunk and disoriented when he arrived, awakening at 7am to find his Toshiba notebook computer, a mobile telephone, an iPod Nano, his Australian passport as well as Visa and Diners Club credit cards missing.

Copies of the CCTV footage at the hotel had been forwarded to Australian officials in Bangkok.

The investigation is being overseen by the Australian Defence Force Investigative Services, a defence department spokesman told AAP.

The Australian Defence Department has downplayed the theft, saying the laptop contained only the lowest classification and was fitted with appropriate security software to deny access to any information on the computer.

But Carl Thayer, a security analyst at the University of NSW, said any breaches in Australia's secure intelligence profile could lead to a "withdrawal of information (from other countries), a penalty for not keeping it secure".

AAP