FIRST ON 7: A Seven News investigation has revealed some of Sydney's most peaceful, law-abiding suburbs are awash with guns, part of a statewide stash of nearly a million weapons.

They are perfectly legal, registered and meant to be kept safe; but the fear is that some are falling into the wrong hands.

More than 700,000 legal firearms are stored in homes across New South Wales. They belong to target shooters, hunters and collectors.

"[It's] a well-kept secret you might say. It is very, very popular," the Sporting Shooters' Association's Mitch Newbury said.

Now a Seven News investigation can reveal the key Sydney suburbs where our residential arsenal is stored.

Gosford on the Central Coast is home to more than 5000 firearms, Camden 4300, Liverpool 3800 and Campbelltown just under 3000.

Inner Sydney has surprising numbers too, Maroubra, Dee Why and Eastgardens have 1,200 each, Mosman more than a 1000, and Turramurra 900.

"I know there are some individuals that have got 20 firearms or more," Bankstown Gun Shop's Steve Ballas said.

"Behind their clothes in their walk-in wardrobe, they've got a false wall in there and so on."

It's perfectly legal to own licensed weapons and store them in your home, but details of who owns them, and where they're kept is held on a police data base, and it's the security of that information which is causing concern.

Last week an elderly owner was bashed and robbed of five pistols and four rifles in a deliberately targeted raid, according to police.

Shooters MP Robert Borsak believes the firearms registry may have been breached.

"Well, we think what happened was that great slabs of data came from the encrypted system and downloaded onto the police intranet," Mr Borsak said.

In 2010, the risk of a leak was identified, but now only a few hundred police have access.

"Originally all police, sworn-unsworn, had access to that database," Assistant NSW Police Commissioner Alan Clarke said.

"It was a broad arrangement, that certainly has been changed now."