By Jason Palmer
Science and technology reporter, BBC News, Prague
Mobiles are ubiquitous but few share the same essential software
The widespread outbreak of mobile phone viruses will occur when a sufficient number of them share an operating system (OS), according to researchers.
Viruses spread by Bluetooth could reach all users of a given OS in days, whereas those spread by multimedia messages could spread in just hours.
But the virulence will only appear when a given OS has about 10% market share.
This "percolation transition" was described at the Science Beyond Fiction conference in Prague.
In 2008, Albert-Laszlo Barabasi, Director of the Center for Complex Network Research at Northeastern University in the US, published a study on the movements of more than 100,000 mobile phone users.
Their daily routines showed which "social networks" an individual user inhabits, and their patterns of movement exhibited surprising repetition and predictability.
Now, Professor Barabasi and his team have turned their attention to how these networks could facilitate the proliferation of mobile viruses.
"There are actually more than 600 mobile phone viruses out there," Prof Barabasi told BBC News. What is more, he explained, mobile phone viruses have reached a level of sophistication in two years that computer viruses took more than two decades to achieve.
"But why haven't I ever got one?" he asked.
Mobile viruses can spread in two ways: through Bluetooth, or via a file sent as a multimedia message.
"You have to have the right operating system; the viruses that will spread on the iPhone will not spread on Nokias, and vice versa," said Prof Barabasi.
"It turns out that the Bluetooth way, because it's driven by human mobility, is relatively slow. If you launch a Bluetooth virus it may take anywhere from days to months to spread, particularly if it's not a popular phone."
Mobile viruses have struck when lots of people gather
Eventually users take infected phones to shops and replace or reset them, or change phones altogether, and the viruses spread no further.
"The real question is about MMS viruses. They're instantaneous: within two minutes everyone in your address book could have it; within a few hours everyone who is reachable would have it."
To discover the reason that this hasn't happened, the team turned to the network theory that was used in the 2008 work, making use of the data set that showed them the details of users' movement and social connections.
In the network theory, there is a phenomenon known as a "percolation transition".
In social networks, beyond the transition, everyone is connected to everyone. Applied to mobile viruses, the transition describes the point of no return: when everyone who could conceivably have a given virus will get it.
Up to now, viruses transmitted by MMS have spread sufficiently slowly that operators have had a chance to block them. The future scenario will be very different.
"Right now, we're under the percolation threshold. Only 5% of users have smartphones and even those are fragmented into different operating systems - the largest one doesn't even reach 3% of the overall market.
"We predict that once any operating system reaches 10% of the whole user market, then the percolation transition will happen, and then the [viruses] will spread everywhere."
Near the percolation transition of 10% market share, viruses spread via MMS wouldn't necessarily reach every single handset with a given operating system, but they would cast their net before operators will have time to respond.
On the other hand, a Bluetooth-mediated viruses, while having a much slower rate of infection, could conceivably reach every user of a given OS.