"The consequences of any major disruption to Web site availability would be serious for CASA," McLaren said.

"IT could ultimately affect some airline operations both in Australia and overseas, as well as public and government confidence in our organization."

A spokesperson for CASA said the contract is very specific in terms of service level agreements (SLAs) in terms of virus and patching, adding that a planned outage last weekend was proof enough.

"We had our computer room shut down on the weekend for annual cleaning - we moved the Web site to a different server and the e-mails did bank up," the spokesperson said.

"On Saturday, Macquarie noticed this, rang us and said we had a problem; however, we were already on top of it."