Copies of England's bowling tactics for the Australian batsmen were emailed to ABC Radio during the second day of the fourth Ashes Test here Wednesday and were subsequently broadcast during the national broadcaster's cricket coverage.
Cricket Australia said Thursday it was satisfied that security was not breached in or around the players' dressing rooms.
Cricket and security officials also accept that cricket fan Nick Ruthry found the page, which outlined England's bowling tactics for the match, and emailed it to ABC radio.
Ruthry told The Sydney Morning Herald that he found a copy of England's plans on the ground in the members' area on Wednesday.
"I'd heard the ABC (radio) commentators saying they were wondering what the England plans were, so I thought I'd help them out," Ruthry told the newspaper.
But the England and Wales Cricket Board (ECB) said it was continuing to investigate how the document got out.
The ABC made it public during Wednesday's play, adding further embarrassment to England's disastrous Ashes defence.
"From Cricket Australia's point of view, the MCC and local event security have accepted this piece of paper did not come from the player rooms -- there is no breach of security in or around the player rooms," CA spokesman Philip Pope said.
"That's been ruled out and it's an important point.
"It underlines the point that we have very stringent security and the ECB has completely accepted it didn't come from there, in consultation with the ICC anti-corruption officer and indeed our security man down there.
"The MCC and ECB are still discussing, still trying to understand between them, how the piece of paper ostensibly came to be dropped in the members' area.
"That will be a point of discussion between the two parties."