The state government has defended spending $200,000 hunting down the source of embarrassing leaks about budget blowouts in major transport projects by saying it is protecting community safety in an age of global terrorism.

In recent months, the state government has been embarrassed by a string of leaked sensitive cabinet documents relating to cost blowouts of its major infrastructure projects.

But a document released under freedom-of-information laws has revealed it spent nearly $200,000 in one month investigating the source of leaks in a single week in July alone, mostly relating to cost blowouts of the controversial WestConnex Motorway.

But under questioning from the opposition in question time on Tuesday, Transport Minister Andrew Constance said there was a need to investigate "major security breaches" within his department because of rising global cyber and physical terrorism.