The Australian presenter for McAfee, Michael Sentonas, says computers that have been impacted by any type of malicious software could be under control by a user someplace else on the internet.

Infected computers can become "zombies," which send out viruses and spam without their owners significant.

We have a lot of people with high speed broadband connections with more and more online services, connecting to things like Face book and Twitter and other social networks, Mr Sentonas said.

So we are regrettably a good target.

But the head of expertise for antivirus and security firm Sophos, Paul Ducklin, doubts the situation is as bad as McAfee says.

The main movement that 'zombies' or owned computers are used for is sending spam email, Mr Ducklin said.

So if we look at where spam comes from all around the world, that gives us a good signal of which countries have the most infected computers, and the good news is that Australia usually comes in about 40th on the league table.

The US is generally near the top, along with countries like Brazil and India and China, as you would wait for from their populations.