There have been no major outbreaks of computer viruses among smartphones because no smartphone operating system is popular enough to let a virus to spread effectively — yet, a new study suggests.

The data also predict that once a single smartphone operating system gains a critical percentage of the entire mobile phone market, viruses could start to pose "a serious threat" to mobile communications, said the study released Thursday in Science Express.

Smartphones "are poised to become the dominant communication device in the near future, raising the possibility of virus breakouts that could overshadow the disruption caused by traditional computer viruses," said the paper by Pu Wang and other researchers at Northwestern University.

A smartphone virus, like other computer viruses, can only target a single operating system, and different brands of smartphones currently use different operating systems.

The study used the calling patterns and co-ordinates from anonymized billing records of 6.2 million mobile phone subscribers to create computer simulations of virus outbreaks.

They looked at three different methods of transmission between phones:

• Bluetooth, in which viruses can spread to other handsets nearby (within 10 to 30 metres) that also support Bluetooth.
• MMS (multimedia messaging service), in which messages containing the virus are sent to contacts in the infected phone's address book.
• A hybrid method, in which a single virus can spread both ways.

The results show that Bluetooth viruses have the potential to reach all susceptible users as the handsets move with their owners, but take days to months to spread through the population, which would likely leave lots of time for people to install antivirus software once an outbreak is detected.

MMS viruses show an "explosive" spread, but currently can only reach a small fraction of people who use a particular operating system. The virus is stopped in its tracks by people who don't have anyone in their address book with the same operating system.

The study predicts that situation will continue until one operator obtains a share of at least 9.5 per cent of the overall mobile market.

Smartphones currently make up about five per cent of the total mobile market, and the most popular smartphone operating system, Symbian, has 64.3 per cent of the smartphone market — that's 3.2 per cent of the mobile market overall.

Bluetooth viruses are also affected by market share. If an operating system has a market share of 10 per cent, it would take months for the virus to reach all susceptible handsets. However, if the operating system has a market share of 30 per cent, it could reach 85 per cent within a few hours, and 99.8 per cent in less than a week, the study reported.

Hybrid viruses that use both spreading methods posed the "most significant danger" but they too are limited by small market shares.

The researchers said they believe their research helps assess the risks associated with mobile viruses and help in the development of measures to avoid future outbreaks.