One of the country's top secret spy agencies is warning Australian businesses to brace for a wave of cyber attacks around next week's G20 summit in Brisbane.

Over recent weeks, the Australian Signals Directorate (ASD) has given an increasing number of briefings to industry about how to avoid G20-linked hacks.

The Canberra-based spy agency warned that because Australia has assumed the chairmanship of the G20, networks here have "become a more attractive target for cyber espionage and attack".

CREST Australia, an organisation which provides cyber and information security advice, said protest groups see online attacks as a much easier option.

Sorry, this video has expired Cyber security stepped up as G20 looms in Brisbane ( Josh Bavas )

The organisation's spokesman Greg Rudd said with so many high profile leaders in the country, next weekend's G20 summit is an irresistible target for hackers.

"They would love to just get into the traffic light system for example and just disrupt that and what they're after really is free international media," Mr Rudd told the ABC's AM program.

In its official G20 cyber security advice, the ASD outlined common techniques used by hackers, including sending emails with malicious software, or hijacking public wi-fi networks.

The ASD also warned gifts such as USB sticks are commonly given at events like the G20 and should be avoided because they can secretly install software which can then steal sensitive data.

"Never use them, never put them in your machine because you'll be putting other things into your computer," Mr Rudd said.

Mr Rudd said there were three broad categories of groups who could launch cyber attacks on the G20: state-sanctioned hackers, commercial spies and activist organisations such as Anonymous.

"Because China is an obvious suspect and Russia is an obvious suspect, a lot of hackers all over the world have gone out of their way and developed it into a bit of an art form to lay the blame at China and Russia's feet for all sorts of hacks," he said.

The Queensland Government has in the last month identified vulnerabilities and upgraded its electronic defence mechanisms to prepare for all scenarios.

Queensland Police Deputy Commissioner Ross Barnett said authorities were are as prepared for any cyber attack as they could be.

"Nothing is impenetrable, but we believe that all of the testing and target-hardening over the last 12 months or so will stand us in good stead," she said.

In 2011, the French finance ministry confirmed it fell victim to a targeted attack during the G20 Summit in Cannes, in which documents related to the French presidency were stolen.

At the London Olympics in 2012, hackers threatened to cut the power supply during the games.

Six major attacks were prevented at the games, including one that nearly cut the internet connection for hundreds of journalists.

Chinese officials were not immune, either.

In 2008, the Beijing Olympics took about 500,000 attempted probes on their network every hour.